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{{Infobox weapon
|is_ranged=yes
|name= Rifle, 5.56 mm, M16
|image= [[File:M16a1m16a2m4m16a45wi.jpg|260px]]
|caption= From top to bottom: M16A1, M16A2, [[M4 carbine|M4A1]], M16A4
|origin= {{flag|United States}}
|type= [[Assault rifle]]
|design_date= 1957
|designer= [[Eugene Stoner]] and [[L. James Sullivan]]<ref>{{Cite journal|title = Focus on Basics, Urges Small Arms Designer |first=Virginia Hart |last=Ezell |authorlink= |month=November |year=2001 |journal = National Defense |publisher=[[National Defense Industrial Association]] |url = http://www.nationaldefensemagazine.org/archive/2001/November/Pages/Focus_on4174.aspx }}</ref>
|manufacturer= <li>{{flagicon|USA}} [[Colt's Manufacturing Company|Colt Defense]] <li>{{flagicon|Republic of Korea}} [[S&T Daewoo|Daewoo Precision Industries]] <li>{{flagicon|Belgium}} [[FN Herstal]] <li>{{flagicon|USA}} [[H & R Firearms]] <li>{{flagicon|USA}} [[General Motors]] [[Hydramatic]] Division<li>{{flagicon|Philippines}} [[Elisco]]<li>{{flagicon|USA}} [[U.S. Ordnance]]
|production_date= 1960–present
|service= 1963–present
|used_by= See ''[[#Users|Users]]''
|wars= [[Vietnam War]] <br>[[Invasion of Grenada]]<br>[[Gulf War]]<br>[[Somali Civil War]]<br>[[Operation Deny Flight]] <br>[[Operation Joint Endeavor]]<br>[[War in Afghanistan (2001–present)]]<br>[[Iraq War]]
|spec_type= [[Selective fire]]/[[assault rifle]]
|spec_label= M16A2
|part_length= {{convert|20|in|mm|0|abbr=on}}
|cartridge= [[5.56×45mm NATO]]
|feed system= 20- and 30-round box magazine, or 100-round drum
|action= [[Gas-operated reloading|Gas-operated]], [[rotating bolt]] ([[direct impingement]])
|rate= 12–15 rounds/min sustained<br>45–60 rounds/min semi-automatic<br>700–950 rounds/min cyclic
|velocity= 3,110 ft/s (948 m/s)<ref>[http://web.archive.org/web/20110725160425/http://www.colt.com/mil/M16_2.asp M15 5.56mm Rifle. Specifications]. colt.com</ref>
|range= 550 meters (point target)<br>800 meters (area target)
|weight= 7.18 lbs (3.26 kg) (unloaded) <br>{{convert|8.79|lb|kg|sigfig=2|abbr=on}} (loaded)
|length= {{convert|39.5|in|mm|sigfig=3|abbr=on}}
|variants= See ''[[#Variants|Variants]]''
|number= ~8 million<ref name="coltcustomers"/>
}}

The '''M16''' (officially '''Rifle, Caliber 5.56&nbsp;mm, M16''') is the United States military designation for the [[AR-15]] rifle adapted for semi-automatic, three-round burst and full-automatic fire. [[Colt's Manufacturing Company|Colt]] purchased the rights to the AR-15 from [[ArmaLite]], and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the [[5.56×45mm NATO]] cartridge. The rifle entered [[United States Army]] service and was deployed for [[jungle warfare]] operations in [[South Vietnam]] in 1963,<ref>Rose, pp. 380 & 392.</ref> becoming the U.S. military's standard [[service rifle]] of the [[Vietnam War]] by 1969,<ref>Urdang, p. 801.</ref> replacing the [[M14 rifle]] in that role. The U.S. Army retained the M14 in [[CONUS]], [[Europe]], and [[South Korea]] until 1970. Since the Vietnam War, the M16 rifle family has been the primary service rifle of the U.S. armed forces.

The M16 has also been widely adopted by other militaries around the world. Total worldwide production of M16-style weapons since the design's inception has been approximately 8 million, making it the most-produced firearm of its caliber.<ref name="Colt Weapon Systems">[http://www.colt.com/mil/M16.asp Colt Weapon Systems].</ref> As of 2010, the M16 is being phased out in the United States Army, and is being replaced by the [[M4 carbine]], which is itself a shortened derivative of the M16A2.<ref name="SmallArmsIndividual">{{cite web|title=Small Arms–Individual Weapons|url=http://www.fas.org/man/dod-101/sys/land/wsh2011/290.pdf |accessdate=8 November 2010 |date=3 |month=November |year=2010}}</ref> In US Army service, the M16 could be supplemented by the [[Individual Carbine]] beginning in 2014 if procurement of a new weapon is attained, if funds allow. All other US services would stay with current M16s and M4 series weapons.<ref name="possible IC replacement">{{cite web |title=Improved carbines headed your way |url=http://www.armytimes.com/news/2011/04/army-improved-carbines-heading-your-way-043011w/ |publisher=Gannett Government Media Corporation |author=Lance M. Bacon |date=30 April 2011 |accessdate=30 April 2011}}</ref>

==Introduction==
The M16 is a lightweight, 5.56&nbsp;mm, air-cooled, [[Gas-operated reloading|gas-operated]], [[Magazine (firearm)|magazine]]-fed [[assault rifle]], with a [[rotating bolt]], actuated by [[direct impingement]] gas operation. The rifle is made of steel, [[7075 aluminium alloy|7075 aluminum alloy]], composite plastics and polymer materials.

In the early 1960s, the [[United States Air Force|U.S. Air Force]]'s rifle, the M16, and the Army's XM16E1, were the first versions of the M16 rifle fielded. Soon the U.S. Army standardized an upgrade of the XM16E1 as the M16A1 rifle, an M16 with a [[forward assist]] feature and other improvements requested by the Army. All of the early versions were chambered to fire the M193/M196 cartridge in the [[Semi-automatic firearm|semi]]-automatic and the [[Automatic firearm|automatic]] firing modes. This occurred in the early 1960s, with the Army issuing it in late 1964.<ref name="Venola">{{Cite journal| surname=Venola | given=Richard| title=What a Long Strange Trip It's Been |journal=Book of the AR-15 |volume=1 |issue=2 |year=2005 |pages=6–18 }}</ref> Commercial AR-15s were first issued to Special Forces troops in spring of 1964.<ref>{{Cite book|first=Daniel |last=Ford |title=The Only War We've Got: Early Days in South Vietnam |year=2001 |isbn=9780595175512 |url=http://books.google.com/?id=sV_K3L6hTqEC}}</ref>

[[Image:M40 gasmask.jpg|thumb|left|A U.S. soldier on NBC exercise, holding an M16A1 rifle and wearing an [[M40 Field Protective Mask]]. Note the receiver, [[forward assist]] and the barrel flash suppressor.]]

The M16A2 rifle entered service in the 1980s, being ordered in large scale by 1987, chambered to fire the standard [[NATO]] cartridge, the Belgian-designed M855/M856 cartridge.<ref name="Venola"/> The M16A2 is a select-fire rifle (semi-automatic fire, three-round-burst fire) incorporating design elements requested by the Marine Corps:<ref name="Venola"/> an adjustable, windage rear-sight; a stock {{convert|5/8|in|mm}} longer; heavier barrel; case deflector for left-hand shooters; and cylindrical handguards.<ref name="Venola"/> The fire mode selector is on the receiver's left side.

The M16A3 rifle is an M16A2 rifle with an M16A1's fire control group (semi-automatic fire, automatic fire) that is used only by the U.S. Navy.

The M16A4 rifle was standard issue for the [[United States Marine Corps]] in [[Iraq War|Operation Iraqi Freedom]] since 2004; it replaced the M16A2 in front line units. In the U.S. Army the M16A2 rifle is being supplemented with two rifle models, the M16A4 and the [[M4 carbine]] as the standard issue assault rifle. The M16A4 has a flat-top receiver developed for the M4 carbine, a handguard with four [[Picatinny rail]]s for mounting a sight, [[laser]], [[night vision device]], forward handgrip, removable handle, or a flashlight.

The M16 rifle is principally manufactured by [[Colt Firearms|Colt]] and [[Fabrique Nationale de Herstal]] (under a U.S. military contract since 1988 by FNH-USA; currently in production since 1991, primarily M16A2, A3, and A4), with variants made elsewhere in the world. Versions for the U.S. military have also been made by [[H & R Firearms]]<ref>[http://www.hr1871.com/about/ H&R "About Us" page].</ref> [[General Motors]] [[Hydramatic]] Division<ref>[http://www.thegunzone.com/556dw-5.html The Gun Zone].</ref> and most recently by [[Sabre Defence]].<ref>[http://www.defensereview.com/sabre-defence-industries-awarded-m16-rifle-contract-m16a3-m16a4-rifles/ Sabre Defence Industries Awarded M16 Rifle Contract].</ref> Semi-automatic versions of the AR-15 are popular recreational shooting rifles, with versions manufactured by other small and large manufacturers in the U.S.<ref>[http://www.ar-15.us/AR15_Manufacturers.php AR15 Manufacturers & Builders].</ref>

==History==
===Summary===
[[Image:M16A1 PVS-2.JPEG|right|thumb|The XM16E1 is seen here fitted with an AN/PVS-2 night vision scope.]]

ArmaLite sold its rights to the AR-15 to Colt in 1959.<ref>p.96 Dockery, Kevin ''Future Weapons'' Berkley Books, 2007</ref> The AR-15 was first adopted in 1962 by the [[United States Air Force]], ultimately receiving the designation ''M16''. The U.S. Army began to field the ''XM16E1'' en masse in 1965 with most of them going to the [[Republic of Vietnam]], and the newly organized and experimental [[Airmobile]] Divisions, the [[1st Air Cavalry Division]] in particular. The U.S. Marine Corps in South Vietnam also experimented with the M16 rifle in combat during this period. The XM16E1 was standardized as the ''M16A1'' in 1967. This version remained the primary infantry rifle of U.S. forces in South Vietnam until the end of the war in 1975, and remained with all U.S. military ground forces after it had replaced the [[M14 rifle|M14]] [[service rifle]] in 1970 in [[CONUS]], Europe (Germany), and South Korea; when it was supplemented by the ''M16A2''. During the early 1980s a roughly standardized load for this ammunition was adopted throughout [[NATO]] (see: ''[[5.56x45mm NATO]]'').

The ''M16A3'' is a fully automatic variant of the M16A2, issued within the [[United States Navy]]. The M16A2 is currently being supplemented by the ''M16A4'', which incorporates the flattop receiver unit developed for the M4 carbine, and [[Picatinny rail]] system. M16A2s are still in stock with the U.S. Army and Marine Corps, but are used primarily by reserve and National Guard units as well as by the U.S. Air Force.{{Citation needed|date=November 2009}}

The M16 rifle design, including variant or modified version of it such as the [[Armalite]]/Colt [[AR-15]] series, AAI M15 rifle; AP74; EAC J-15; SGW XM15A; any 22-caliber rimfire variant, including the Mitchell M16A-1/22, Mitchell M16/22, Mitchell CAR-15/22, and AP74 Auto Rifle, is a prohibited and restricted weapon in Canada.<ref>[http://www.canlii.org/en/ca/laws/regu/sor-98-462/latest/sor-98-462.html Regulations Prescribing Certain Firearms and other Weapons, Components and Parts of Weapons, Accessories, Cartridge Magazines, Ammunition and Projectiles as Prohibited or Restricted, SOR/98-462]. Canlii. 29-06-2010</ref>

The first issues of the rifle generated considerable controversy because the gun suffered from a jamming flaw known as “failure to extract,” which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out the muzzle.<ref name=Reliable>{{cite journal|author=C.H. Chivers|title= How Reliable is the M16 Rifle?|journal=[[New York Times]]|date=November 2, 2009|url=http://atwar.blogs.nytimes.com/2009/11/02/how-reliable-is-the-m-16-rifle/}}</ref> According to a congressional report, the jamming was caused primarily by a change in gunpowder which was done without adequate testing and reflected a decision for which the safety of soldiers was a secondary consideration.<ref>{{cite book|author=David Maraniss|title=They Marched Into Sunlight: War and Peace Vietnam and America October 1967|url=http://books.google.com/books?id=qftwHKSnmpkC|year=2003|publisher=Simon and Schuster|isbn=9780743262552|page=[http://books.google.com/books?id=qftwHKSnmpkC&pg=PA410 410]}}</ref> Due to the issue, reports of soldiers being wounded were directly linked to the M16, which many soldiers felt was unreliable compared to its precursor, the [[M14]], which used stick powder, varying from the M16's utilization of ball powder.

===Project SALVO===

<!-- This section is linked from [[Assault rifle]] -->
[[File:National Firearms Museum, Vietnam-era rifles.jpg|thumb|An M16 (third from top), an AR-10 and a second M16 along with other Vietnam War era rifles.]]

In 1948, the Army organized the civilian [[Operations Research Office]], mirroring similar [[operations research]] organizations in the United Kingdom. One of their first efforts, Project ALCLAD, studied [[ballistic vest|body armor]] and the conclusion was that they would need to know more about battlefield injuries in order to make reasonable suggestions.<ref name = "SAOW"/> Over 3 million battlefield reports from World War I and World War II were analyzed and over the next few years they released a series of reports on their findings.<ref name = "SAOW"/>

The conclusion was that most combat takes place at short range. In a highly mobile war, combat teams ran into each other largely by surprise; and the team with the higher firepower tended to win. They also found that the chance of being hit in combat was essentially random; accurate "aiming" made little difference because the targets no longer sat still. The number one predictor of casualties was the total number of bullets fired.<ref name="SAOW">{{Cite book|last=Ezell |first=Edward Clinton |title= Small Arms of the World|year= 1983|publisher= Stackpole Books|location=New York |isbn=978-0880296014|pages=46–47 }}</ref> Other studies of behavior in battle revealed that many U.S. infantrymen (as many as 2/3) never actually fired their rifles in combat. By contrast, soldiers armed with rapid fire weapons were much more likely to have fired their weapons in battle.<ref name="SLAM">{{Cite book|last=Marshall|first=S. L. A. |title= Men against Fire:The Problem of Combat Command in Future War |year=1966 |publisher=[[William Morrow and Company]] |location=New York City |pages=50–60 }}</ref> These conclusions suggested that infantry should be equipped with a fully automatic rifle of some sort in order to increase the actual firepower of regular soldiers. It was also clear, however, that such weapons dramatically increased ammunition use and in order for a rifleman to be able to carry enough ammunition for a firefight he would have to carry something much lighter.

Existing rifles met none of these criteria. Although it appeared the new 7.62&nbsp;mm T44 (precursor to the [[M14 rifle|M14]]) would increase the rate of fire, its heavy 7.62&nbsp;mm NATO cartridge made carrying significant quantities of ammunition difficult. Moreover, the length and weight of the weapon made it unsuitable for short range combat situations often found in jungle and urban combat or mechanized warfare, where a smaller and lighter weapon could be brought to bear faster.

[[Image:M16A1 brimob.jpg|thumb|left|M16A1]]

These efforts were noticed by Colonel [[René Studler]], U.S. Army Ordnance's Chief of Small Arms Research and Development. Col. Studler asked the [[Aberdeen Proving Ground]] to submit a report on the smaller caliber weapons. A team led by Donald Hall, director of program development at Aberdeen, reported that a .22&nbsp;inch (5.56&nbsp;mm) round fired at a higher velocity would have performance equal to larger rounds in most combat.<ref name="DHALL">{{Cite book|last=Hall|first=Donald L. |title= An Effectiveness Study of the Infantry Rifle |year=1952 |url=http://handle.dtic.mil/100.2/AD377335 |publisher= Army Ballistic Research Lab, Aberdeen Proving Ground|location=Maryland}}</ref> With the higher rate of fire possible due to lower recoil it was likely such a weapon would inflict more casualties on the enemy. His team members, notably William C. Davis,&nbsp;Jr. and Gerald A. Gustafson, started development of a series of experimental .22 (5.56&nbsp;mm) cartridges. In 1955, their request for further funding was denied.

A new study, Project SALVO, was set up to try to find a weapon design suited to real-world combat. Running between 1953 and 1957 in two phases, SALVO eventually suggested that a weapon firing four rounds into a {{convert|20|in|mm|sigfig=3|adj=on}} area would double the hit probability of existing semi-automatic weapons.

In the second phase, SALVO II, several experimental weapons concepts were tested. Irwin Barr of [[AAI Corporation]] introduced a series of [[flechette]] weapons, starting with a shotgun shell containing 32 darts and ending with single-round flechette "rifles". [[Winchester Repeating Arms Company|Winchester]] and [[Springfield Armory]] offered [[Multiple Barrel Firearm|multiple barrel]] weapons, while ORO's own design used two .22, .25 or .27 caliber bullets loaded into a single [[.308 Winchester]] or [[.30-06 Springfield|.30-06]] cartridge.

===Eugene Stoner===
[[Image:Hawaii-convoy2003-12-17.jpg|thumb|right|A U.S. soldier with M16A2 at [[Schofield Barracks]], Hawaii. The [[United States Army]] did not place a large order for the A2 model until 1986.]]

Meanwhile testing of the 7.62&nbsp;mm T44 continued, and [[Fabrique Nationale de Herstal|Fabrique Nationale]] also submitted their new [[FN FAL]] via the American firm Harrington & Richardson as the T48. The T44 was selected as the new battle rifle for the U.S. Army (rechristened the M14) despite a strong showing by the T48.{{Citation needed|date=November 2009}}

In 1954, [[Eugene Stoner]] of the newly formed [[ArmaLite]] helped develop the 7.62&nbsp;mm [[AR-10]]. Springfield's T44 and similar entries were conventional rifles using wood for the "furniture" and otherwise built entirely of steel using mostly forged and machined parts. ArmaLite was founded specifically to bring the latest in designs and alloys to firearms design, and Stoner felt he could easily beat the other offerings.

The AR-10's receiver was made of [[Forging|forged]] and [[Milling machine|milled]] aluminium alloy instead of steel. The barrel was mated to the receiver by a separate hardened steel extension to which the bolt locked. This allowed a lightweight aluminum receiver to be used while still maintaining a steel-on-steel lockup. The bolt was operated by high-pressure combustion gases taken from a hole in the middle of the barrel directly through a tube above the barrel to a cylinder created in the bolt carrier with the bolt carrier itself acting as a piston. Traditional rifles located this cylinder and piston close to the gas vent. The [[Stock (firearm)|stock]] and grips were made of a [[glass-reinforced plastic]] shell over a rigid foam plastic core. The [[muzzle brake]] was fabricated from [[titanium]]. Over Stoner's objections, various experimental composite and 'Sullaloy' aluminum barrels were fitted to some AR-10 prototypes by ArmaLite's president, George Sullivan. The Sullaloy barrel was made entirely of heat-treated aluminum, while the composite barrels used aluminum extruded over a thin stainless steel liner.

Meanwhile the layout of the weapon itself was also somewhat different. Previous designs generally placed the sights directly on the barrel, using a bend in the stock to align the sights at eye level while transferring the recoil down to the shoulder. This meant that the weapon tended to rise when fired making it very difficult to control during fully automatic fire. The ArmaLite team used a solution previously used on weapons such as the [[Nazi Germany|German]] [[FG 42]] and [[M1941 Johnson machine gun|Johnson light machine gun]]; they located the barrel in line with the stock, well below eye level, and raised the sights to eye level. The rear sight was built into a carrying handle over the receiver.

Despite being over {{convert|2|lb|kg|abbr=on}} lighter than the competition, the AR-10 offered significantly greater accuracy and recoil control. Two prototype rifles were delivered to the U.S. Army's Springfield Armory for testing late in 1956. At this time, the U.S. armed forces were already two years into a service rifle evaluation program, and the AR-10 was a newcomer with respect to older, more fully developed designs. Over Stoner's continued objections, George Sullivan had insisted that both prototypes be fitted with composite aluminum/steel barrels. Shortly after a composite barrel burst on one prototype in 1957, the AR-10 was rejected. The AR-10 was later produced by a Dutch firm, Artillerie Inrichtingen, and saw limited but successful military service with several foreign nations such as Sudan, Guatemala, and Portugal. Portugal deployed a number of AR-10s for use by its airborne (''Caçadores Pára-quedista'') battalions, and the rifle saw considerable combat service in [[Portuguese Colonial Wars|Portugal's counter-insurgency campaigns]] in Angola and Mozambique.<ref>Afonso, Aniceto and Gomes, Carlos de Matos, ''Guerra Colonial'' (2000), ISBN 972-46-1192-2, pp. 183–184.</ref> Some AR-10 rifles were still in service with airborne forces serving during the withdrawal from Portuguese Timor in 1975.

===CONARC===
In 1957, a copy of Gustafson's funding request from 1955 found its way into the hands of General [[Willard G. Wyman]], commander of the U.S. Continental Army Command. He immediately put together a team to develop a .223 caliber (5.56&nbsp;mm) weapon for testing. Their finalized request called for a select-fire weapon of {{convert|6|lb|kg}} when loaded with 20 rounds of ammunition. The bullet had to penetrate a standard U.S. steel [[M1 Helmet|helmet]], body armor, or a steel plate of {{convert|0.135|in|mm}} and retain a velocity in excess of the speed of sound at {{convert|500|yd|m}}, while equaling or exceeding the "wounding" ability of the [[.30 Carbine]].<ref name="SAOW"/><ref>Hutton, Robert (ed.), ''The .223'', Guns & Ammo Annual Edition, 1971.</ref>

Wyman had seen the AR-10 in an earlier demonstration, and impressed by its performance he personally suggested that ArmaLite enter a weapon for testing using a 5.56&nbsp;mm cartridge designed by Winchester.<ref name="SAOW"/> Their first design, using conventional layout and wooden furniture, proved to be too light. When combined with a conventional stock, recoil was excessive in fully automatic fire. Their second design was simply a scaled-down AR-10, and immediately proved much more controllable. Winchester entered the [[Winchester LMR|LMR]],<ref>[http://www.securityarms.com/20010315/galleryfiles/1800/1863.htm Winchester Lmr]. Securityarms.com. Retrieved on 2011-09-27.</ref> a design based loosely on their [[M1 carbine]], and Earle Harvey of Springfield attempted to enter a design, but was overruled by his superiors at Springfield, who refused to divert resources from the T44. In the end, ArmaLite's [[AR-15]] had no competition. The lighter round allowed the rifle to be scaled down, and was smaller and lighter than the previous AR-10. The AR-15 weighed only around {{convert|5.5|lb|kg}} empty, and {{convert|6|lb|kg}} loaded (with a 20 round magazine).

During testing in March 1958, rainwater caused the barrels of both the ArmaLite and Winchester rifles to burst, causing the Army to once again press for a larger round, this time at {{convert|0.258|in|mm|abbr=on}}. Nevertheless, they suggested continued testing for cold-weather suitability in Alaska. Stoner was later asked to fly in to replace several parts, and when he arrived he found the rifles had been improperly reassembled. When he returned he was surprised to learn that they too had rejected the design even before he had arrived; their report also endorsed the {{convert|0.258|in|mm|abbr=on}} round. After reading these reports, General [[Maxwell Taylor]] became dead-set against the design, and pressed for continued production of the M14.

Not all the reports were negative. In a series of mock-combat situations testing the AR-15, [[M14 rifle|M14]] and [[AK-47]], the Army found that the AR-15's small size and light weight allowed it to be brought to bear much more quickly, just as CONARC had suggested. Their final conclusion was that an 8-man team equipped with the AR-15 would have the same firepower as a current 11-man team armed with the M14. U.S. troops were able to carry more than twice as much [[5.56×45mm]] ammunition as 7.62x51mm for the same weight, which would allow them a better advantage against a typical [[Vietnam People's Army|NVA]] unit armed with AK-47s.

At this point, [[Fairchild Aircraft|Fairchild]] had spent $1.45 million in development expenses, and wished to divest itself of its small-arms business. Fairchild sold production rights for the AR-15 to [[Colt Firearms]] in December 1959, for only $75,000 cash and a 4.5% royalty on subsequent sales; Robert W. MacDonald of Cooper-MacDonald got a finder's fee of $250,000 and a 1% royalty for arranging the deal.<ref>{{Harvnb|M16 Rifle Review Panel|1968|p=D-5}}</ref> In 1960, ArmaLite was reorganized, and Stoner left the company.

===M16 adoption===
[[Curtis LeMay]] viewed a demonstration of the AR-15 in July 1960. In the summer of 1961, General LeMay had been promoted to the position of USAF Chief of Staff, and requested an order of 80,000 AR-15s for the U.S. Air Force.<ref name="Rose, p. 372">Rose, p. 372.</ref> However under the recommendation of General [[Maxwell D. Taylor]], who advised the Commander in Chief that having ''two'' different calibers within the military system at the same time would be problematic, President [[John F. Kennedy|Kennedy]] turned down the request.<ref name="Rose, p. 372"/> However, [[DARPA|Advanced Research Projects Agency]], which had been created in 1958 in response to the Soviet [[Sputnik]] program, embarked on [[project AGILE]] in the spring of 1961. AGILE's priority mission was to devise inventive fixes to the communist problem in South Vietnam. In October 1961, William Godel, a senior man at ARPA, sent 10 AR-15s to South Vietnam to let the allies test them. The reception was enthusiastic, and in 1962 another 1,000 AR-15s were sent to South Vietnam.<ref>Rose, pp. 372–373.</ref> [[Special Operations]] units and advisers working with the South Vietnamese troops filed battlefield reports lavishly praising the AR-15 and the stopping effectiveness of the 5.56&nbsp;mm cartridge, and pressed for its adoption. However, what no one knew, except the men directly using the AR-15s in Vietnam, were the devastating kills<ref name="Rose, p. 373">Rose, p. 373.</ref> made by the new rifle, photographs of which, showing enemy casualties made by the .223 (5.56&nbsp;mm) bullet remained classified into the 1980s.<ref name="Rose, p. 373"/>

The damage caused by the .223 (5.56mm) "varmint"<ref name="Rose, p. 373"/> bullet was observed and originally believed to be caused by "tumbling" due to the slow 1 in {{convert|14|in|mm|adj=on}} rifling twist rate.<ref name="ar15oracle01">[http://ammo.ar15.com/ammo/project/term_tighttwist.html :: Ammo Oracle]. Ammo.ar15.com. Retrieved on 2011-09-27.</ref> However, this twist rate only made the bullet less stable in air.<ref name="ar15oracle01"/> Any pointed lead core bullet will turn base over point ("tumble") after penetration in flesh, because the center of gravity is aft of the center of the projectile.<ref name="ar15oracle01"/> The large wounds observed by soldiers in Vietnam were actually caused by projectile fragmentation, which was created by a combination of the projectile's velocity and construction.<ref name="ar15oracle01"/>

U.S. [[Secretary of Defense]] Robert McNamara now had two conflicting views: the ARPA report favoring the AR-15 and the Pentagon's position on the M14. Even President [[John F. Kennedy]] expressed concern, so McNamara ordered Secretary of the Army [[Cyrus Vance]] to test the M14, the AR-15 and the AK-47. The Army's test report stated only the M14 was suitable for Army use, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used, who reported that the testers showed favor to the M14.

[[Image:101st Airborne Division - Vietnam 03.jpg|thumb|upright|left|U.S. Soldier cleans his XM16E1 during the [[Vietnam War]] in 1966.]]

Secretary Robert McNamara ordered a halt to M14 production in January 1963, after receiving reports that M14 production was insufficient to meet the needs of the armed forces. Secretary McNamara had long been a proponent of weapons program consolidation among the armed services. At the time, the AR-15 was the only rifle that could fulfill a requirement of a "universal" infantry weapon for issue to all services. McNamara ordered the weapon be adopted unmodified, in its current configuration, for immediate issue to all services, despite receiving reports noting several deficiencies with the M16 as a service rifle, including the lack of a [[Chrome plating|chrome-lined]] bore and chamber, the 5.56&nbsp;mm projectile's instability under arctic conditions,{{Citation needed|date=November 2009}} and the fact that large quantities of 5.56&nbsp;mm ammunition required for immediate service were not available.{{Citation needed|date=November 2009}} In addition, the Army insisted on the inclusion of a [[forward assist]] to help push the bolt into battery in the event that a cartridge failed to seat in the chamber through fouling or corrosion. Colt had argued the rifle was a self-cleaning design, requiring little or no maintenance. Colt, Eugene Stoner, and the U.S. Air Force believed that a forward assist needlessly complicated the rifle, adding about $4.50 to its procurement cost with no real benefit. As a result, the design was split into two variants: the Air Force's M16 without the forward assist, and for the other service branches, the XM16E1 with the [[forward assist]].

In November 1963, McNamara approved the Army's order of 85,000 XM16E1s for jungle warfare operations;<ref>Rose, pp. 380, 392.</ref> and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s.<ref name="SAOW"/><ref>Rose, p. 380.</ref> Meanwhile, the Army carried out another project, the Small Arms Weapons Systems, on general infantry firearm needs in the immediate future. They recommended the immediate adoption of the weapon. Later that year the Air Force officially accepted their first batch as the United States Rifle, Caliber 5.56&nbsp;mm, M16.

The Army immediately began to issue the XM16E1 to infantry units but the rifle was initially delivered without adequate cleaning supplies or instructions. When the M16 reached [[Vietnam]] with U.S. troops in March 1965, reports of stoppages in combat began to surface. Often the gun suffered from a stoppage known as “failure to extract,” which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out the muzzle.<ref name="Reliable"/> Although the M14 featured a [[Chrome plating|chrome-lined]] barrel and chamber to resist corrosion in combat conditions, neither the bore nor the chamber of the M16/XM16E1 was chrome-lined. Several documented accounts of troops killed by enemy fire with inoperable rifles broken-down for cleaning eventually brought a Congressional investigation.<ref name="Time Under Fire">[http://www.time.com/time/magazine/article/0,9171,843858,00.html "Defense: Under Fire"]. Time Magazine, 9 June 1967.</ref>

{{cquote|We left with 72 men in our platoon and came back with 19, Believe it or not, you know what killed most of us? Our own rifle. Practically every one of our dead was found with his [M16] torn down next to him where he had been trying to fix it.<br/>- Marine Corps Rifleman, Vietnam.<ref name="Time Under Fire"/>}}

The root cause of the stoppages turned out to be a problem with the powder for the ammunition. In 1964 when the Army was informed that [[DuPont]] could not mass-produce the nitrocellulose-based powder to the specifications demanded by the M16, the [[Olin Corporation|Olin Mathieson Company]] provided a high-performance ball propellant of nitrocellulose and nitroglycerin. While the Olin WC 846 powder was capable of firing an M16 5.56&nbsp;mm round at the desired {{convert|3300|ft|m|abbr=on}} per second, it had the unintended consequence of increasing the automatic rate of fire from 850 to 1000 rounds per minute. This would leave behind dirty residue, making the M16 more likely to have a stoppage. The problem was resolved by fitting the M16 with a buffer system, slowing the rate of fire back down to 650 to 850 rounds per minute and outfitting all newly produced M16s with an anti corrosive chrome-plated chamber.<ref>[http://www.time.com/time/magazine/article/0,9171,899755,00.html Defense: Powder Pains] Time Magazine, 8 September 1967.</ref>

On February 28, 1967, the XM16E1 was standardized as the M16A1. Major revisions to the design followed. The rifle was given a chrome-lined chamber (and later, the entire bore) to eliminate corrosion and stuck cartridges, and the rifle's recoil mechanism was re-designed to accommodate Army-issued 5.56&nbsp;mm ammunition. Rifle cleaning tools and powder solvents/lubricants were issued. Intensive training programs in weapons cleaning were instituted, and a [[comic book]] style manual was circulated among the troops to demonstrate proper maintenance.<ref name="SAOW"/> The reliability problems of the M16 diminished quickly, although the rifle's reputation continued to suffer.<ref name="SAOW"/>

According to a February 1968 [[United States Department of Defense|Department of Defense]] report the M16 rifle achieved widespread acceptance by U.S. troops in Vietnam. Only 38 of 2100 individuals queried wanted to replace the M16 with another weapon. Of those 38, 35 wanted the [[CAR-15]] (a shorter version of the M16) instead.<ref>Maj. Bruce F. Kay [http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA044796&Location=U2&doc=GetTRDoc.pdf An Analysis of Infantry's Need for an Assault Submachine Gun], Master of Military Art and Science thesis. University of Nebraska. Final Report 10 June 1977. p. 34.</ref>

===NATO standards===
[[Image:Bundeswehr shooting M16.jpg|thumb|right|[[German Army]] soldiers of the 13th Panzergrenadier Division qualify with the M16A2 at [[Würzburg]], as part of a partnership range with the [[U.S. 1st Infantry Division]].]]
[[File:Stanag mags.jpg|thumb|right|Vietnam era 20-round magazine (left) and Current issue NATO STANAG 30-round magazine (right).]]

In March 1970, the U.S. stated that all [[NATO]] forces should eventually adopt the [[5.56x45mm]] cartridge. This shift represented a change in the philosophy of the military's long-held position about caliber size. By the middle of the 1970s, other armies were also looking at M16-style weapons. A NATO standardization effort soon started, and tests of various rounds were carried out starting in 1977. The U.S. offered their original 5.56x45mm design, the M193, with no modifications, but there were concerns about its penetration in the face of the wider introduction of [[ballistic vest|body armor]]. In the end the Belgian 5.56x45mm SS109 round was chosen ([[STANAG]] 4172). Their round was based on the U.S. cartridge but included a new 62 grain bullet design with a small steel tip added to improve penetration. The U.S. Marine Corps was first to adopt the round with the M16A2, introduced in 1982. This was to become the standard U.S. military rifle. The NATO 5.56x45mm standard ammunition produced for U.S. forces is designated [[M855]].

Shortly after NATO's acceptance of the [[5.56x45mm NATO]] rifle cartridge in October 1980.<ref>Watters,Daniel: "[http://www.thegunzone.com/556dw-8.html The 5.56 X 45mm Timeline: A Chronology of Development]", The Gun Zone, 2000–2007.</ref> Draft Standardization Agreement 4179 ([[STANAG 4179]]) was proposed in order to allow the military services of member nations easily to share rifle [[ammunition]] and [[magazine (firearm)|magazines]] during operations, at the individual soldier level, in the interest of easing logistical concerns. The magazine chosen to become the '''[[STANAG magazine]]''' was originally designed for the U.S. M16 rifle. Many NATO member nations, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However the standard was never ratified and remains a 'Draft STANAG'<ref>"[http://www.dtic.mil/ndia/2008Intl/Arvidsson.pdf NATO Infantry Weapons Standardization]", NDIA Conference 2008</ref>

The [[NATO Accessory Rail]] STANAG 4694, or [[Picatinny rail]] STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles in order to provide a standardized mounting platform. The rail comprises a series of ridges with a T-shaped cross-section interspersed with flat "spacing slots". Scopes are mounted either by sliding them on from one end or the other; by means of a "rail-grabber" which is clamped to the rail with bolts, thumbscrews or levers; or onto the slots between the raised sections. The rail was originally for scopes. However, once established, the use of the system was expanded to other accessories, such as tactical lights, laser aiming modules, night vision devices, [[reflex sight]]s, foregrips, bipods, and bayonets.

All current M16 type rifles are capable of launching NATO STANAG type 22mm [[rifle grenade]]s from their integral flash hiders without the use of an adapter. These 22&nbsp;mm grenade types range from powerful anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. They come in the "standard" type which are propelled by a blank cartridge inserted into the chamber of the rifle. They also come in the "bullet trap" and "shoot through" types, as their names imply use live ammunition. The U.S. military does not generally use rifle grenades, however they are used by other Nations.

Currently, the M16 is in use by 15 NATO countries and more than 80 countries world wide.
[[Image:Loading M203.JPEG|right|thumb|Loading an [[M203 grenade launcher|M203 40 mm grenade launcher]] attached to an M16 rifle with a practice round.]]

===Grenade launcher===
The [[M203 grenade launcher|M203 40 mm grenade launcher]] was originally designed to be mounted on the M16 and its variants. It uses the same rounds as the older M79 "shotgun"-type grenade launcher, which utilize High-Low Propulsion System to keep recoil forces low. The M203 is versatile and compatible with many rifle models. It is widely used by the U.S. Military and is routinely seen on the M4 Carbine. The launcher can also be mounted onto the Canadian made C7, and requires the bottom handguard on the rifle to be removed in order to mount the launcher.

==Design==
[[Image:Usafm16.svg|thumb|right|Top drawing is of an A2-style rifle; bottom drawing is of an A2-style rifle with A1 rear sights (as with the [[Colt Canada C7 rifle|C7]])]]
[[File:Combat knife attached to gun.jpg|thumb|right|USMC M16A2s with the [[OKC-3S bayonet|OKC-3S]] bayonet.]]

The M16's receivers are made of [[7075 aluminium alloy|7075 aluminum alloy]], its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics. Early models were especially lightweight at {{convert|6.5|lb|kg}} without magazine and sling. This was significantly less than older 7.62&nbsp;mm "battle rifles" of the 1950s and 1960s. It also compares with the {{convert|6.5|lb|kg}} [[AKM]] without magazine.<ref>weight without magazine of AK (1949) – 3.9 kg, AK (1955) – 3.5 kg, AKM (1959) – 2.9 kg Field manual for AK (Наставление по стрелковому делу 7.62-мм автомат Калашникова (АК)); Field manual for AKM and AKMS (Наставление по стрелковому делу 7.62-мм модернизированный автомат Калашникова (АКМ и АКМС))</ref> M16A2 and later variants (A3 & A4) weigh more ({{convert|8.5|lb|kg|1|abbr=on}} loaded) because of the adoption of a thicker barrel profile. The thicker barrel is more resistant to damage when handled roughly and is also slower to overheat during sustained fire. Unlike a traditional "bull" barrel that is thick its entire length, the M16A2's barrel is only thick forward of the handguards. The barrel profile under the handguards remained the same as the M16A1 for compatibility with the [[M203 grenade launcher]]. The rifle is the same length as the M16A2.

The M16 rifle fires the [[5.56x45mm]] cartridge and can produce massive wounding effects when the bullet impacts at high velocity and yaws in tissue leading to fragmentation and rapid transfer of energy.<ref>''American Rifle: A Biography'', Alexander Rose (2009) p. 375-376</ref><ref>''The SAS Training Manual'', Chris McNab, (2002) pp. 108–109</ref><ref>[http://arxiv.org/abs/0803.3051 "Scientific Evidence for 'Hydrostatic Shock'"], Michael Courtney and Amy Courtney, (2008)</ref> This produces wounds that were so devastating that the International Committee of the Red Cross (ICRC)<ref>International Legal Initiatives to Restrict Military Small Arms Ammunition W. Hays Parks∗ Copyright 2010 by W. Hays Parks International Committee of the Red Cross (ICRC) page 1-18</ref> and many countries (Austria, Argentina, Belgium, Bolivia, Bulgaria, Burundi, Cambodia, Cyprus, Germany, Ireland, Latvia, Lithuania, Luxembourg, Mauritius, Mexico, Romania, Samoa, Slovenia, Sweden, Switzerland, etc.)<ref>International Legal Initiatives to Restrict Military Small Arms Ammunition W. Hays Parks∗
Copyright 2010 by W. Hays Parks International Committee of the Red Cross (ICRC) page 1-18</ref> considered the M16 to be an inhumane weapon.<ref>Ian V. Hogg , Military Small Arms of the 20th Century, 1981</ref><ref>Parks, W. Hays. [http://www.dtic.mil/ndia/2010armament/TuesdayLandmarkBHaysParks.pdf "International Legal Initiatives to Restrict Military Small Arms Ammunition"]. W. Hays Parks International Committee of the Red Cross (ICRC) via DTIC.mil, 2010.</ref>

One distinctive ergonomic feature is a plastic or metal stock directly behind the action, which contains a [[recoil]] spring.<ref name="SAOW2">{{Cite book|last=Ezell |first=Edward Clinton |title= Small Arms of the World|year= 1983|publisher= Stackpole Books|location=New York |isbn=978-0880296014|pages=746–762 }}</ref> This serves the dual function of operating spring and recoil buffer.<ref name="SAOW2"/> The stock being in line with the bore reduces muzzle rise, especially during automatic fire. Because recoil does not significantly shift the point of aim, faster follow-up shots are possible and user fatigue is reduced.

Another distinctive ergonomic feature is a carrying handle on top of the receiver, with an integrated rear sight assembly and charging handle. This design is a by-product of the original design where the carry handle served to protect the charging handle and mount a scope.<ref name="SAOW2"/> In practice, the handle is rarely used to carry the weapon and doing so is expressly prohibited in many military organizations, as it is considered unsafe.{{Citation needed|date=November 2009}} Holding the weapon by the pistol grip provides quicker response time and better "muzzle awareness," while a shoulder sling provides a more convenient option when response time is not a concern. {{Citation needed|date=November 2009}} The "accessory rail" is also considered unsafe to use after the weapon has been fired for prolonged periods as enough heat, to melt flesh, will transfer from the receiver to the handle. More importantly, with the sight plane {{convert|2.5|in|mm|1|abbr=on}} over the bore, the M16 has an inherent [[Parallax#In gunfire|parallax]] problem that can be confounding to shooters. At closer ranges (typically inside 15–20 meters), the shooter must aim high in order to place shots where desired.

Newer models have a "flattop" upper receiver with a [[Picatinny rail]], to which the user can attach either a conventional sighting system or numerous optical devices such as [[night vision]] scopes.

The M16 utilizes [[direct impingement]] [[Gas-operated|gas operation]]; energy from high-pressure gas tapped from a non-adjustable port built into the front sight assembly actuates the moving parts in the weapon. Combustion gases travel via a gas tube above the barrel directly into a chamber in the bolt carrier behind the bolt itself, pushing the carrier away from the bolt. This reduces the number of moving parts by eliminating the need for a separate piston and cylinder and it provides better performance in rapid fire by keeping reciprocating masses on the same axis as the bore.{{Citation needed|date=November 2009}}

The primary criticism of direct impingement is that fouling and debris from expended gunpowder is blown directly into the breech. As the superheated combustion gas travels down the tube, it expands and cools. This cooling causes vaporized matter to condense as it cools depositing a much greater volume of solids into the operating components of the action. The increased fouling can cause malfunctions if the rifle is not cleaned as frequently as should be. The amount of sooting deposits tends to vary with powder specification, caliber, and gas port design.

In April 2010 TACOM Life Cycle Management Command issued permission for soldiers to camouflage M4/M16 weapons with paint if given command approval.<ref name="Camo">{{cite web|last=Dawson|first=D|title=Crib Notes for Soldiers – Weapons Painting 101|url=http://peosoldier.armylive.dodlive.mil/2010/05/14/crib-notes-for-soldiers-%E2%80%93-weapons-painting-101/|accessdate=16 May 2010}}</ref>

==Variants==
{{Details|AR-15 variants|M16 variants}}

===Pre-Production ArmaLite AR-15===
The weapon that eventually became the M16 series only had a vague resemblance to its offspring. The rifle was basically a scaled down [[AR-10]] with an [[Ambidexterity|ambidextrous]] charging handle located within the carrying handle, a narrower front sight "A" frame, and no flash suppressor.<ref>Page 744 "Small Arms of the World" 12th revised Edition by Edward Clinton Ezell.</ref>

===AR-15 (Colt Models 601 & 602)===
{{Main|AR-15}}
Colt's first two models produced after the acquisition of the rifle from ArmaLite were the 601 and 602, and these rifles were in many ways clones of the original ArmaLite rifle (in fact, these rifles were often found stamped ''Colt ArmaLite AR-15, Property of the U.S. Government caliber .223'', with no reference to them being M16s).<ref>Pages 744–759 "Small Arms of the World" 12th Revised Edition by Edward Clinton Ezell.</ref> The 601 and 602 are easily identified by their flat lower receivers without raised surfaces around the magazine well and occasionally green or brown furniture. The 601 was adopted first of any of the rifles by the USAF, and was quickly supplemented with the XM16 (Colt Model 602) and later the M16 (Colt Model 604) as improvements were made. There was also a limited purchase of 602s, and a number of both of these rifles found their way to a number of Special Operations units then operating in South East Asia, most notably the [[United States Navy SEALs|U.S. Navy SEALs]]. The only major difference between the 601 and 602 is the switch from the original 1:14-inch rifling twist to the more common 1:12-inch twist. These weapons were equipped with a triangular charging handle and a bolt hold open device that lacked a raised lower engagement surface. The bolt hold open device had a slanted and serrated surface that had to be engaged with a bare thumb, index finger, or thumb nail because of the lack of this surface.

The United States Air Force continued to use the AR-15 marked rifles in various configurations into the 1990s.

===M16===

Variant originally adopted by the U.S. Air Force. This was the first M16 adopted operationally. This variant had triangular handguards, butt stocks without a compartment for the storage of a cleaning kit,<ref>Page 754 "Small Arms of the World" 12th Revised Edition by Edward Clinton Ezell.</ref> a three-pronged flash suppressor, and no [[forward assist]]. Bolt carriers were originally chrome plated and slick-sided, lacking forward assist notches. Later, the chrome plated carriers were dropped in favor of Army issued notched and [[parkerized]] carriers though the interior portion of the bolt carrier is still chrome-lined. The Air Force continued to operate these weapons until around 2001, at which time the Air Force converted all of its M16s to the M16A2 configuration.

The M16 was also adopted by the [[Special Air Service|British SAS]], who used it to effect during the [[Falklands War]].<ref name="specialoperations1">[http://www.specialoperations.com/Foreign/United_Kingdom/SAS/Weapons.htm Special Operations.com].</ref>

===XM16E1 and M16A1 (Colt Model 603)===
[[Image:M16duckbill.gif|thumb|right|An early M16 rifle: note "duckbill" flash suppressor, triangular grip, forward assist, and the lack of brass deflector]]

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a [[forward assist]] and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967.

To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued while barrels with chrome-plated chambers and later fully lined bores were introduced. The front sight was now a square post with 4 detent positions, adjustable for vertical zeroing by using a cartridge, nail or special tool.

With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such a way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject until corrected. The M16A1 remains in service in limited numbers in the United States but is still standard issue in many world armies.

===M16A2===
[[File:M16A2 - AM.016070.jpg|thumb|right|M16A2]]
[[Image:M16 upper right.jpg|thumb|right|New rear sight, brass deflector and forward assist of M16A2]]
[[Image:TANKSaimingin2041102.jpg|thumb|right|A Marine with an M16A2 on a training exercise at [[Dreamland (Fallujah, Iraq)|Camp Baharia]], Iraq, 2004]]

The development of the M16A2 rifle was originally requested by the [[United States Marine Corps]] as a result of the USMC's combat experience in Vietnam with the XM16E1 and M16A1.<ref name="Venola"/> The Marines were the first branch of the U.S. Armed Forces to adopt the M16A2 in the early/mid 1980s with the [[United States Army]] following suit in the late 1980s. This rifle is now the current issue to Marine Corps' recruits in both MCRD San Diego and MCRD Parris Island. Modifications to the M16A2 were extensive. In addition to the new rifling, the barrel was made with a greater thickness in front of the front sight post to resist bending in the field and to allow a longer period of sustained fire without overheating. The rest of the barrel was maintained at the original thickness to enable the [[M203 grenade launcher]] to be attached.<ref name="Venola"/> A new adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800 meters to take full advantage of the ballistic characteristics of the new SS109 rounds and to allow windage adjustments without the need of a tool or cartridge.<ref name="Venola"/> The flash suppressor was again modified, this time to be closed on the bottom so it would not kick up dirt or snow when being fired from the prone position, and acting as a [[Muzzle brake|recoil compensator]].<ref>{{Cite book|title=Military Small Arms of the 20th Century |page=292 |first=Ian |last=Hogg |coauthors=Weeks, John |year=2000 |publisher=Krause Publications |isbn=9780873418249 |edition=7 |url=http://books.google.com/?id=teAAHt1GaE8C&q=Military+Small+Arms+of+the+20th+Century&dq=Military+Small+Arms+of+the+20th+Century}}</ref> The front grip was modified from the original triangular shape to a round one, which better fitted smaller hands and could be fitted to older models of the M16.<ref name="Venola"/> The new handguards were also symmetrical so that armories need not separate left and right spares. The handguard retention ring was tapered to make it easier to install and uninstall the handguards.<ref name="Venola"/> A notch for the middle finger was added to the pistol grip, as well as more texture to enhance the grip. The buttstock was lengthened by {{convert|5/8|in|mm}}.<ref name="Venola"/> The new buttstock became ten times stronger than the original due to advances in polymer technology since the early 1960s. Original M16 stocks were made from fiberglass-impregnated resin; the newer stocks were engineered from DuPont Zytel glass-filled thermoset polymers. The new stock included a fully textured polymer buttplate for better grip on the shoulder, and retained a panel for accessing a small compartment inside the stock, often used for storing a basic cleaning kit. The heavier bullet reduces [[muzzle velocity]] from {{convert|3200|ft/s|m/s|sigfig=2}}, to about {{convert|3050|ft/s|m/s|sigfig=2}}.{{Citation needed|date=September 2010}} The A2 also uses a faster twist rifling to allow the use of a trajectory-matched tracer round. A spent case deflector was incorporated into the upper receiver immediately behind the ejection port to prevent cases from striking left-handed users.<ref name="Venola"/>

The action was also modified, replacing the fully automatic setting with a three-round burst setting.<ref name="Venola"/> When using a fully automatic weapon, poorly trained troops often hold down the trigger and "spray" when under fire. The U.S. Army concluded that three-shot groups provide an optimum combination of ammunition conservation, accuracy and firepower.

===M16A3===
The M16A3 was a fully automatic variant of the M16A2 adopted in small numbers around the time of the introduction of the M16A2, primarily by the U.S. Navy for use by [[United States Navy SEALs|SEAL]], [[Seabee]], and Security units.<ref name = did/> It features the M16A1 trigger group providing "safe", "semi-automatic", and "fully automatic" modes.

===M16A4===
[[File:USMC M16A4 Rifle.JPG|thumb|right|[[USMC|U.S. Marines]] aboard the [[USS Essex (LHD-2)|USS ''Essex'']] zero their M16A4 rifles]]

The M16A4 is the fourth generation of the M16 series. It is equipped with removable carrying handle, and full length quad picatinny rail for mounting optics and other ancillary devices. The Colt M16A4 model RO945, using safe/semi/burst selective fire, is now the standard issue for front-line U.S. Marine Corps and some U.S. Army units.<ref name=did>{{Cite news|url=http://www.defenseindustrydaily.com/the-usas-m-16-rifle-purchases-04517/ |title=US Navy, Marines Buy M-16 Rifles |date=2 January 2008 |work=Defense Industry Daily}}</ref>

Military issue rifles are also equipped with a [[Knight's Armament Company]] M5 RAS hand guard, allowing vertical grips, lasers, tactical lights, and other accessories to be attached, coining the designation M16A4 MWS (or Modular Weapon System) in U.S. Army field manuals.<ref name=globalsecurity>{{Cite book|url=http://www.globalsecurity.org/military/library/policy/army/fm/3-22-9/c02.htm#2_1 |title=US Army Field Manual: RIFLE MARKSMANSHIP M16A1, M16A2/3, M16A4 and M4 CARBINE |date=24 April 2003}}</ref>

Colt also produces M16A4 models for international purchases, with specifics selective fire:
*R0901 / NSN 1005-01-383-2872 (Safe/Semi/Auto)
*R0905 (Safe/Semi/Burst)

==Derivatives==
===Colt Model 655 and 656 "Sniper" variants===
With the expanding [[Vietnam War]], Colt developed two rifles of the M16 pattern for evaluation as possible light sniper or designated marksman rifles. The Colt Model 655 M16A1 Special High Profile was essentially a standard A1 rifle with a heavier barrel and a scope mount that attached to the rifle's carry handle. The Colt Model 656 M16A1 Special Low Profile had a special upper receiver with no carrying handle. Instead, it had a low-profile iron sight adjustable for windage and a Weaver base for mounting a scope, a precursor to the Colt and Picatinny rails. It also had a hooded front iron sight in addition to the heavy barrel. Both rifles came standard with either a Leatherwood/Realist scope 3–9× Adjustable Ranging Telescope. Some of them were fitted with a Sionics noise and flash suppressor. Neither of these rifles were ever standardized.

These weapons can be seen in many ways to be predecessors of the U.S. Army's [[United States Army Squad Designated Marksman Rifle|SDM-R]] and the USMC's [[U.S. Marine Corps Squad Advanced Marksman Rifle|SAM-R]] weapons.

===XM177===
{{Main|CAR-15}}
[[File:USAF GAU-5A.jpg|thumb|right|A [[United States Air Force|USAF]] GAU-5/A carbine.]]

In Vietnam, some soldiers were issued a [[carbine]] version of the M16 called the [[CAR-15|XM177]]. The XM177 had a shorter {{convert|10|in|mm|0|abbr=on}} barrel and a telescoping stock, which made it substantially more compact. It also possessed a combination flash hider/sound moderator to reduce problems with muzzle flash and loud report. The USAF's GAU-5/A (XM177) and the U.S. Army's XM177E1 variants differed over the latter’s inclusion of a forward assist, although some GAU-5s do have the forward assist. The final USAF GAU-5A/A and U.S. Army XM177E2 had an {{convert|11.5|in|mm|0|abbr=on}} barrel with a longer flash/sound suppressor. The lengthening of the barrel was to support the attachment of Colt's own [[XM148 grenade launcher|XM148]] 40&nbsp;mm grenade launcher. These versions were also known as the Colt Commando model commonly referenced and marketed as the CAR-15. The variants were issued in limited numbers to special forces, helicopter crews, Air Force pilots, Air Force Security Police Military Working Dog (MWD) handlers, officers, radio operators, artillerymen, and troops other than front line riflemen. Some USAF GAU-5A/As were later equipped with even longer {{convert|14.5|in|mm|adj=on}} 1/12 rifled barrels as the two shorter versions were worn out. The {{convert|14.5|in|mm|adj=on}} barrel allowed the use of MILES gear and for bayonets to be used with the sub-machine guns (as the USAF described them). By 1989 the USAF started to replace the earlier barrels with 1/7 rifled models.

Also used by the British [[Special Air Service|SAS]], who used it to effect during the [[Falklands War]].<ref name="specialoperations1"/>

===Colt Model 733===
Colt also returned to the original "[[CAR-15|Commando]]" idea, with its Model 733, essentially a modernized XM177E2 with many of the features introduced on the M16A2.

===M231 Firing Port Weapon (FPW)===
[[Image:M231 1.svg|thumb|left|M231 FPW]]
[[M231 Firing Port Weapon|M231 Firing Port Weapon (FPW)]] is an adapted version of the M16 assault rifle for firing from ports on the [[M2 Bradley]]. The infantry's normal M16s are too long for use in a "buttoned up" APC, so the FPW was developed to provide a suitable weapon for this role. Designed by the Rock Island Arsenal, the M231 FPW remains in service, although all but the rear two firing ports on the Bradley have been removed. The M231 FPW is often used by dismounted [[Mechanized Infantry]] during trench clearing and [[MOUT]] operations due to its compact size and high rate of fire. The M231 FPW fires from the open bolt and is only configured for fully automatic fire. The open bolt configuration gives the M231 a much higher cyclic rate of fire than the closed bolt operation of the M16A1.

===Mk 4 Mod 0===
The Mk 4 Mod 0 was a variant of the M16A1 produced for the U.S. Navy SEALs during the Vietnam War and adopted in April 1970. It differed from the basic M16A1 primarily in being optimized for maritime operations and coming equipped with a sound suppressor. Most of the operating parts of the rifle were coated in [[Kal-Guard]], a hole of {{convert|0.25|in|mm}} was drilled through the stock and buffer tube for drainage, and an O-ring was added to the end of the buffer assembly. The weapon could reportedly be carried to the depth of 200 feet (60 m) without damage. The initial Mk 2 Mod 0 Blast Suppressor was based on the U.S. Army's Human Engineering Lab's (HEL) M4 noise suppressor. The HEL M4 vented gas directly from the action, requiring a modified bolt carrier. A gas deflector was added to the charging handle to prevent gas from contacting the user. Thus, the HEL M4 suppressor was permanently mounted though it allowed normal semi-automatic and automatic operation. If the HEL M4 suppressor were removed, the weapon would have to be manually loaded after each single shot. On the other hand, the Mk 2 Mod 0 blast suppressor was considered an integral part of the Mk 4 Mod 0 rifle, but it would function normally if the suppressor were removed. The Mk 2 Mod 0 blast suppressor also drained water much more quickly and did not require any modification to the bolt carrier or to the charging handle. In the late 1970s, the Mk 2 Mod 0 blast suppressor was replaced by the Mk 2 blast suppressor made by Knight's Armament Company (KAC). The KAC suppressor can be fully submerged and water will drain out in less than eight seconds. It will operate without degradation even if the M16A1 is fired at the maximum rate of fire. The U.S. Army replaced the HEL M4 with the much simpler Studies in Operational Negation of Insurgency and Counter-Subversion (SIONICS) MAW-A1 noise and flash suppressor.

===Mark 12===
{{Main|United States Navy Mark 12 Mod X Special Purpose Rifle}}
Developed to increase the effective range of soldiers in the designated marksman role, the US Navy developed the Mark 12 Special Purpose Rifle (SPR). Configurations in service vary, but the core of the Mark 12 SPR is an 18" heavy barrel with muzzle brake and free float tube. This tube relieves pressure on the barrel caused by standard handguards and greatly increases the potential accuracy of the system. Also common are higher magnification optics ranging from the 6× power Trijicon ACOG to the Leupold Mark 4 Tactical rifle scopes. Firing Mark 262 Mod 0 ammunition with a 77gr Open tip Match bullet, the system has an official effective range of 600+ meters. However published reports of confirmed kills beyond 800 m from Iraq and Afghanistan are not uncommon.{{Citation needed|date=May 2010}}

===M4 carbine===
{{Main|M4 carbine}}
[[Image:SCRange20034344940.jpg|thumb|right|An [[M4 carbine#M4A1|M4A1 carbine]] (foreground) and two M16A2s (background) being fired by U.S. Marines during a [[live fire exercise]]: though adopted in the 1990s and derived from the M16A2, the M4 carbine was part of a long line of short-barreled [[AR-15]] used in the U.S. military]]
[[Image:Calgary Highlanders Exercise Black Bear 2004.jpg|right|thumb|[[Canadian Forces]] Reserve infantrymen train in urban operations with C7 and C8 rifles.]]

The M4 carbine was developed from various outgrowths of these designs, including a number of {{convert|14.5|in|mm|0|adj=on}}-barreled A1 style carbines. The XM4 (Colt Model 727) started its trials in the mid-1980s, with a barrel of {{convert|14.5|in|mm}}. Officially adopted as a replacement for the [[M3 submachine gun|M3 "Grease Gun"]] (and the [[M9 pistol|Beretta M9]] and M16A2 for select troops) in 1994, it was used with great success in the Balkans and in more recent conflicts, including the [[War in Afghanistan (2001–present)|Afghanistan]] and [[United States invasion of Iraq|Iraq]] theaters. The M4 carbine has a three-round [[Burst mode (firearm)|burst]] firing mode, while the M4A1 carbine has a [[Automatic firearm|fully automatic]] firing mode. Both have a [[Picatinny rail]] on the upper receiver, allowing the carry handle/rear sight assembly to be replaced with other sighting devices.

===International derivatives===
====C7 and C8====
{{Main|Colt Canada C7 rifle}}

The [[Diemaco]] [[Colt Canada C7 rifle|C7]] and C8 are updated variants of the M16 developed and used by the [[Canadian Forces]] and are now manufactured by [[Colt Canada]]. The C7 is a further development of the experimental M16A1E1. Like earlier M16s, it can be fired in either single shot or automatic mode, instead of the burst function selected for the M16A2. The C7 also features the structural strengthening, improved handguards, and longer stock developed for the M16A2. Diemaco changed the trapdoor in the buttstock to make it easier to access and a spacer of {{convert|0.5|in|mm}} is available to adjust stock length to user preference. The most easily noticeable external difference between American M16A2s and Diemaco C7s is the retention of the A1 style rear sights. Not easily apparent is Diemaco's use of hammer-forged barrels. The Canadians originally desired to use a heavy barrel profile instead.

The C7 has been developed to the C7A1, with a [[Weaver rail]] on the upper receiver for a C79 optical sight, and to the C7A2, with different furniture and internal improvements. The Diemaco produced Weaver rail on the original C7A1 variants does not meet the M1913 'Picatinny' standard, leading to some problems with mounting commercial sights. This is easily remedied with minor modification to the upper receiver or the sight itself. Since Diemaco's acquisition by Colt to form Colt Canada, all Canadian produced flattop upper receivers are machined to the M1913 standard.

The C8 is the carbine version of the C7.<ref>[http://www.casr.ca/101-army-smallarm-1.htm Canadian Forces Automatic Rifles]. Canadian American Strategic Review. Retrieved: 2009-08-23.</ref> The C7 and C8 are also used by [[Hærens Jegerkommando]], [[Marinejegerkommandoen]] and [[Forsvarets Spesialkommando (FSK)|FSK]] (Norway), [[Military of Denmark]] (all branches), the [[Royal Netherlands Army]] and [[Netherlands Marine Corps]] as its main infantry weapon. Following trials, variants became the weapon of choice of the British [[Special Air Service|SAS]].

====Others====
*The Chinese [[Norinco CQ]] is an unlicensed derivative of the M16A1 made specifically for export, with the most obvious external differences being in its handguard and [[revolver]]-style pistol grip.

*[[Khaybar KH2002]], is an [[Iran]]ian [[bullpup]] conversion of the locally produced S-5.56 rifle. Iran intends to replace the standard issue weapon of its armed forces with the Khaybar. The S-5.56 assault rifle itself is an Iranian M16 derivative based on the Norinco CQ. Two versions of the S-5.56 include the S-5.56A1, used for M-193-type bullets while the S-5.56A3 is used for SS-109-type bullets.

*The [[MSSR rifle]] developed as an effective, low cost sniper rifle by the [[Philippine Marine Corps]] [[Philippine Marine Corps#Marine Scout Snipers|Scout Snipers]]. The [[Special Operations Assault Rifle (SOAR)]] assault carbine was developed by [[Ferfrans]] based on the M16 rifle. It is used by the [[Special Action Force]].

*[[Republic of China Army|Taiwan]] uses piston-driven M16-based weapons as their standard rifle. These include the [[T65 assault rifle|T65]], [[T86 assault rifle|T86]] and [[T91 assault rifle]]s.

===Summary===
{| class="wikitable"
|-
! Colt model no.
! Military designation
! Barrel Length
! Barrel
! Handguard type
! Buttstock type
! Pistol grip type
! Lower receiver type
! Upper receiver type
! Rear sight type
! Front sight type
! Muzzle device
! Forward assist?
! Case deflector?
! Bayonet lug?
! Trigger pack
|-
|601
|AR-15
|20 in (508&nbsp;mm)
|A1 profile (1:14 twist)
|Green or brown full-length triangular
|Green or brown fixed A1
|A1
|A1
|A1
|A1
|A1
|Duckbill flash suppressor
|No
|No
|Yes
|Safe-Semi-Auto
|-
|602
|AR-15 or XM16
|20 in (508&nbsp;mm)
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Duckbill or three-prong flash suppressor
|No
|No
|Yes
|Safe-Semi-Auto
|-
|603
|XM16E1
|20 in (508&nbsp;mm)
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Three-prong or M16A1 birdcage flash suppressor
|Yes
|No
|Yes
|Safe-Semi-Auto
|-
|603
|M16A1
|20 in (508&nbsp;mm)
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|M16A1-style birdcage flash suppressor
|Yes
|No
|Yes
|Safe-Semi-Auto
|-
|604
|M16
|20 in (508&nbsp;mm)
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Three-prong or M16A1-style birdcage flash suppressor
|No
|No
|Yes
|Safe-Semi-Auto
|-
|645
|M16A1E1/PIP
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A1
|A1 or A2
|A1 or A2
|A1 or A2
|A2
|M16A1 or M16A2-style birdcage flash suppressor
|Yes
|Yes or No
|Yes
|Safe-Semi-Auto or Safe-Semi-Burst
|-
|645
|M16A2
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|A2
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Yes
|Safe-Semi-Burst
|-
|645E
|M16A2E1
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|Flattop with Colt Rail
|Flip-up
|Folding
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Yes
|Safe-Semi-Burst
|-
|N/A
|M16A2E2
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length semi-beavertail w/ HEL guide
|Retractable ACR
|ACR
|A2
|Flattop with Colt rail
|None
|A2
|ACR muzzle brake
|Yes
|Yes
|Yes
|Safe-Semi-Burst
|-
|646
|M16A2E3/M16A3
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|A2
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Yes
|Safe-Semi-Auto
|-
|655
|M16A1 Special High Profile
|20 in (508&nbsp;mm)
|HBAR profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|M16A1-style birdcage flash suppressor
|Yes
|No
|Yes
|Safe-Semi-Auto
|-
|656
|M16A1 Special Low Profile
|20 in (508&nbsp;mm)
|HBAR profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1 with modified Weaver base
|Low Profile A1
|Hooded A1
|M16A1-style birdcage flash suppressor
|Yes
|No
|Yes
|Safe-Semi-Auto
|-
|945
|M16A2E4/M16A4
|20 in (508&nbsp;mm)
|A2 profile (1:7 twist)
|Full-length ribbed or KAC M5 RAS
|Fixed A2
|A2
|A2
|Flattop with MIL-STD-1913 rail
|None
|A4
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Yes
|Safe-Semi-Burst
|-
! Colt model no.
! Military designation
! Barrel Length
! Barrel
! Handguard type
! Buttstock type
! Pistol grip type
! Lower receiver type
! Upper receiver type
! Rear sight type
! Front sight type
! Muzzle device
! Forward assist?
! Case deflector?
! Bayonet lug?
! Trigger pack
|}

==Production and users==
The M16 is the most commonly manufactured 5.56x45 mm rifle in the world. Currently, the M16 is in use by 15 NATO countries and more than 80 countries world wide. Together, numerous companies in the United States, Canada, and China have produced more than 8,000,000 rifles of all variants. Approximately 90% are still in operation.<ref name="coltcustomers">[http://www.colt.com/mil/customers.asp Customers / Weapon users], Colt Weapon Systems.</ref> The M16 replaced the [[M14 rifle|M14]] and [[M1 carbine]] as standard infantry rifles of the U.S. armed forces. The M14 continues to see limited service, mostly in [[sniper]], [[designated marksman]], and ceremonial roles.

===Users===
<!-- Deleted image removed: [[File:COMANF.jpg|thumb|right|[[Brazilian Marine Corps]]. {{pufc|COMANF.jpg}}]] -->
[[Image:Canadian C7A2 Rifle.JPG|thumb|right|A [[Canadian Army]] soldier fires the current issue C7A2 rifle at the range with a C79A2 sight. This particular example is missing the standard TRIAD mount.]]
[[File:Flickr - Israel Defense Forces - Female Soldiers Practice Shooting (1).jpg|thumb|Female soldiers of the [[Israel Defense Forces]] practice shooting]]
[[Image:US Marine M16A4 Rifle ACOG.jpg|thumb|right|U.S. Marine firing an M16A4 equipped with an [[Advanced Combat Optical Gunsight|ACOG]].]]
[[File:CARAT Malaysia 2008 (080715-N-4431B-568).jpg|thumb|right|Malaysian Army soldier with an M16A1 equipped with an [[M203 grenade launcher]] during a CARAT Malaysia 2008.]]
[[File:Monaco-military-02.JPG|thumb|[[Monaco|Monegasque]] carabinier with M16 rifle.]]
[[File:RP Marines assault line DM-SD-06-10463.JPEG|thumb|Philippine Marines using M16A1 rifles with M16A2 foregrips during a military exercise.]]
[[File:Palestinian militant with rifle.png|thumb|right|hochkant|Palestine arab militant with M16 rifle wearing a [[Keffiyeh]] around his head (2009)]]
<!-- READ FIRST: This section is for cited entries only. Please do not add entries into this list without a citation from a reliable source. All entries without a citation will be removed. Thank you.-->

*{{Flag|Afghanistan}}<ref>{{Cite news|url=http://www.foxnews.com/story/0,2933,315121,00.html |first=Justin |last=Fishel |title=U.S. Military to Provide Afghan Army With M-16 Rifles |work=FOXNews.com |date=2007-12-04}}</ref>
*{{Flag|Argentina}}: Special Forces used M16A1 in the Falklands and they currently use the M16A2.<ref>[http://web.archive.org/web/20090122004105/http://saorbats.com.ar/GaleriaSaorbats/EA05/EA05/index.html Exposición del Ejército Argentino en Palermo, Buenos Aires- Mayo de 2005]. saorbats.com.ar</ref>
*{{Flag|Australia}}<ref>{{cite web|url=http://www.diggerhistory.info/pages-weapons/allied_recent.htm |title=Australian weapons, Viet Nam and since |publisher=Diggerhistory.info |date=2002-11-11 |accessdate=2010-08-22}}</ref> M16A1 used and replaced 1989 by the [[Steyr AUG|F88 Au Steyr]]
*{{Flag|Bahrain}}<ref>{{cite report |title=Report of the Bahrain Independent Commission of Inquiry |publisher=Bahrain Independent Commission of Inquiry |url=http://files.bici.org.bh/BICIreportEN.pdf |date=23 November 2011}}</ref>{{rp|pages=77,236,262}}
*{{Flag|Bangladesh}}: Used by the military, special forces and counter terrorism units.<ref>{{cite web|url=http://www.bdmilitary.com/index.php?option=com_content&view=article&id=71&Itemid=95 |title=Small Arms &#124; Bangladesh Military Forces &#124; BDMilitary.com – The voice of the Bangladesh Armed Forces |publisher=BDMilitary.com |date= |accessdate=2010-08-22}}</ref>
*{{Flag|Barbados}}<ref name="ewen2005">Jane's Special Forces Recognition Guide, Ewen Southby-Tailyour (2005) p. 446</ref>
*{{Flag|Belize}}<ref name="ewen2005"/>
*{{Flag|Bolivia}}<ref name="ewen2005"/>
*{{Flag|Bosnia and Herzegovina}} Used by Bosnian Army {{citation needed|date=April 2012}}
*{{Flag|Brazil}}<ref name="ewen2005"/>
*{{Flag|Brunei}}<ref name="ewen2005"/>
*{{Flag|Cambodia}}<ref name="worldpolicy2000">{{cite web|url=http://www.worldpolicy.org/projects/arms/reports/smallarms.htm |title=Report: Profiling the Small Arms Industry – World Policy Institute – Research Project |year=November 2000 |publisher=World Policy Institute |accessdate=2010-07-15}}</ref><ref>[http://www.smallarmssurvey.org/files/sas/publications/w_papers_pdf/WP/WP4_Cambodia.pdf Working Papers]. Small Arms Survey (2011-05-05). Retrieved on 2011-09-27.</ref> M16A1 is used.
*{{Flag|Cameroon}}<ref name="ewen2005"/>
*{{Flag|Canada}}: [[Colt Canada C7 rifle|C7]] and C8 variants made by [[Colt Canada]] is used by the [[Canadian Forces]].<ref name="miller2001">Miller, David (2001). ''The Illustrated Directory of 20th Century Guns''. Salamander Books Ltd. ISBN 1-84065-245-4.</ref>
*{{Flag|Chile}}<ref name="ewen2005"/>
*{{Flag|Costa Rica}}<ref>{{Cite news|url=http://www.colt.com/mil/customers.asp}}</ref>
*{{Flag|Democratic Republic of the Congo}}<ref name="worldpolicy2000"/>
*{{Flag|Denmark}}:<ref name="ewen2005"/> [[Colt Canada C7 rifle|C7]] and C8 variants made by Colt Canada are used by all branches of the [[Danish Defence]].
*{{Flag|Dominican Republic}}<ref name="ewen2005"/>
*{{Flag|East Timor}}<ref>''Jane's Sentinel Security Assessment – Southeast Asia''. Issue 20 – 2007. Pages 146 and 152.</ref>
*{{Flag|Ecuador}}<ref name="ewen2005"/>
*{{Flag|El Salvador}}<ref name="ewen2005"/> M16A1/A2 is used.
*{{Flag|Estonia}}<ref>{{cite web|url=http://www.mil.ee/?menu=tehnika1&sisu=m16a1 |title=Eesti Kaitsevägi – Tehnika – Automaat M-16 A1 |publisher=Mil.ee |date= |accessdate=2008-09-08}}</ref>
*{{Flag|Fiji}}<ref name="ewen2005"/>
*{{Flag|France}}<ref name="ewen2005"/>
*{{Flag|Gabon}}<ref name="ewen2005"/>
*{{Flag|Ghana}}<ref name="ewen2005"/>
*{{Flag|Greece}}<ref name="ewen2005"/> M16A2/M4 is used by the Special forces of the [[Hellenic Army]] ISAF Forces in Afghanistan and [[Hellenic Navy]]
*{{Flag|Grenada}}<ref name="ewen2005"/>
*{{Flag|Guatemala}}<ref name="worldpolicy2000"/> M16A1 is used.
*{{Flag|Haiti}}<ref name="worldpolicy2000"/>
*{{Flag|Honduras}}<ref name="gander1995">Gander, Terry J.; Hogg, Ian V. ''Jane's Infantry Weapons 1995/1996''. Jane's Information Group; 21 edition (May 1995). ISBN 978-0710612410.</ref>
*{{Flag|India}}<ref name="ewen2005"/>
*{{Flag|Indonesia}}<ref name="ewen2005"/>
*{{Flag|Iraq}}: Used by [[Iraqi army]].<ref>{{Cite news| url=http://news.bbc.co.uk/2/hi/middle_east/6665759.stm | work=BBC News | title=First steps to arming Iraq's soldiers | date=2007-05-18 | accessdate=2010-05-12}}</ref>
*{{Flag|Israel}}<ref>{{cite web|author=John Pike |url=http://www.globalsecurity.org/org/news/2003/031217-uzi.htm |title=Israel's army phases out country's iconic Uzi submachine gun |publisher=Globalsecurity.org |date=2003-12-17 |accessdate=2010-08-22}}</ref>
*{{Flag|Jamaica}}<ref name="ewen2005"/>
*{{Flag|Jordan}}<ref name="ewen2005"/>
*{{Flag|Republic of Korea}}: During [[Vietnam War]], [[United States]] provided 27,000 M16 rifles to [[Republic of Korea Armed Forces]] in [[Vietnam]]. Also, 600,000 M16A1s (Colt Model 603K) were manufactured under license by [[S&T Daewoo|Daewoo Precision Industries]]. The delivery started in 1974 and ended in 1985.<ref name="ewen2005"/>
*{{Flag|Lebanon}}<ref name="worldpolicy2000"/><ref name="mcnab2002">{{cite book |editor1-first=Charles C. |editor1-last=Unwin |editor2-first=Mike R. |editor2-last=Vanessa U. |title=20th Century Military Uniforms |year=2002 |edition=2nd |publisher=Grange Books |location=Kent |isbn=1840132763}}</ref>
*{{Flag|Lesotho}}<ref name="ewen2005"/>
*{{Flag|Liberia}}<ref name="worldpolicy2000"/>
*{{flag|Lithuania}}: [[Lithuanian Armed Forces]].<ref>{{cite web|url=http://kariuomene.kam.lt/lt/ginkluote_ir_karine_technika/automatiniai_sautuvai/automatinis_sautuvas_m-16.html |title=Lietuvos kariuomenė :: Ginkluotė ir karinė technika » Automatiniai šautuvai » Automatinis šautuvas M-16 |publisher=Kariuomene.kam.lt |date=2009-04-17 |accessdate=2010-08-22}} {{lt icon}}</ref>
*{{Flag|Malaysia}}<ref name="ewen2005"/>
*{{Flag|Mexico}}<ref name="ewen2005"/>
*{{Flag|Monaco}}<ref>http://ireport.cnn.com/docs/DOC-701167?ref=feeds%2Foncnn</ref>
*{{Flag|Morocco}}<ref name="ewen2005"/>
*{{Flag|New Zealand}}<ref name="ewen2005"/> M16 was used and was replaced in 1988 by [[Steyr AUG]]
*{{Flag|Nepal}}<ref>{{Cite news| url=http://news.bbc.co.uk/2/hi/south_asia/2631939.stm | work=BBC News | title=Nepal takes delivery of US rifles | date=2003-01-06 | accessdate=2010-05-12}}</ref>
*{{Flag|Netherlands}}: [[Colt Canada C7 rifle|C7]] and [[Colt Canada C7 rifle#C8|C8]] variants are used by the [[Royal Netherlands Army]].<ref name="miller2001"/>
*{{Flag|Nicaragua}}<ref name="ewen2005"/>
*{{Flag|Nigeria}}<ref name="ewen2005"/>
*{{Flag|Oman}}<ref name="ewen2005"/>
*{{Flag|Pakistan}}: [[Special Service Group]] (SSG) of the [[Pakistan Army]].<ref>{{cite web|url=http://www.pakdef.info/pakmilitary/army/regiments/ssg.html |title=Pakdef.info&nbsp;— Pakistan Military Consortium: Special Service Group |publisher=Saad, S.; Ali, M.; Shabbir, Usman |year=1998 |accessdate=2009-08-15}}</ref>
*{{Flag|Panama}}<ref name="ewen2005"/> M16A1 is used.
*{{Flag|Peru}}<ref name="ewen2005"/>
*{{Flag|Philippines}}: Manufactured under license by Elisco Tool and Manufacturing.<ref name="ewen2005"/>
*{{Flag|Qatar}}<ref name="ewen2005"/>
*{{Flag|Senegal}}<ref>{{Cite news| url=http://news.bbc.co.uk/2/hi/africa/7392685.stm | work=BBC News | title=Army seeks Senegal ear-choppers | date=2008-05-09 | accessdate=2010-05-12}}</ref>
*{{Flag|Singapore}}: Local variant of the M16A1 (M16S1) manufactured under license by ST Kinetics.<ref name="worldpolicy2000"/>
*{{Flag|Somalia}}<ref name="ewen2005"/>
*{{Flag|South Africa}}<ref name="ewen2005"/>
*{{Flag|Sri Lanka}}<ref name="worldpolicy2000"/>
*{{Flag|South Vietnam}}: 6,000 M16 and 938,000 M16A1, 1966-1975<ref>Walter, John, [http://books.google.se/books?id=Eq2Dnj4sDZIC&pg=PA41 Rifles of the World], Krause Publications, 2006, illustrated 3rd edition, ISBN 0896892417, p. 41</ref>
*{{Flag|Sweden}} A small number of M16A2's are used by the [[Swedish Armed Forces]] for familiarization training <ref>http://www.soldf.com/utlvap.html</ref> (as well as a similar number of AKM's), but they are not issued to combat units
*{{Flag|Thailand}}<ref name="ewen2005"/>
*{{Flag|Tunisia}}<ref name="ewen2005"/>
*{{Flag|Turkey}}<ref name="ewen2005"/> M16A1/A2/A4 variants is used.
*{{Flag|Uganda}}<ref name="ewen2005"/>
*{{Flag|United Arab Emirates}}<ref name="ewen2005"/>
*{{Flag|United Kingdom}}: [[Special Air Service]].<ref>{{cite web|last=Poyer |first=Joe |url=http://world.guns.ru/assault/as18-e.htm |title=Modern Firearms – AR-15 M16 M16A1 M16A2 M16A3 assault rifle |publisher=World.guns.ru |date= |accessdate=2010-08-22}}</ref>
*{{Flag|United States}}<ref>{{cite web|url=http://www.army.mil/factfiles/equipment/individual/m16.html |title=M-16 Rifle Fact File for the United States Army |publisher=Army.mil |date= |accessdate=2010-08-22}}</ref>
*{{Flag|Uruguay}}<ref name="ewen2005"/>
*{{Flag|Vietnam}}<ref name="ewen2005"/> Used captured M16A1 rifles.
<!--
Provide a verifiable source for additions to the Users list above.
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==Future replacement==
Previous attempts by the U.S. Military to replace the M16 were unsuccessful or only supplemented it. The M4 carbine will eventually replace the M16 rifle in the United States Army.

===Background===
Throughout the 1970s, the Army experimented with various materials to replace [[brass]] in cartridge casings. Brass has a number of qualities that make it almost ideal for a cartridge, including low friction against steel, making it easier to extract, and the ease with which casings can be manufactured. However, brass is also dense and expensive, so replacing it could lower both the cost and weight of the ammunition.

Aluminum and steel were popular materials for complete rounds, and AAI successfully developed a plastic blank. Completely caseless ammunition was also studied on several occasions, notably the German 4.7&nbsp;mm designs, and this concept is now being continued with the [[Lightweight Small Arms Technologies]] Program.

[[Image:Colt ACR.jpg|thumb|right|Colt ACR/M16A2E2 fitted with [[C79 optical sight|ELCAN C79]] scope (second from top to bottom)]]

Later in the 1980s, the [[Advanced Combat Rifle]] program was run to find a replacement for the M16. Colt entered a modified M16A2 known as the Colt ACR, which used duplex rounds, a system that lowered recoil by 40% to improve repeating shots, and added a 3.5x scope. This weapon, designated M16A2E2, also featured a "guide" of sorts as part of a special handguard developed by the [[United States Army Research Laboratory|U.S. Army Human Engineering Laboratory]] designed to assist in snap-shooting, and a carbine style stock very similar to the recent stock developed by the [[Naval Surface Warfare Center Crane Division]].

The [[Steyr ACR]] used new flechette ammunition that was nominally called 5.56&nbsp;mm, with a very high {{convert| 4750|ft/s|0|abbr=on}} muzzle velocity. Other variants experimented with [[caseless ammunition]] technologies as well.

===Replacement designs===
In the 1980s, the [[M249 light machine gun|M249]] was issued to infantry units, replacing some [[M60 machine gun|M60]]s and some M16A1s at the squad level. In the 1990s the [[M4 carbine]] took over the operational role of the [[M3 submachine gun]], some [[M9 pistol|M9s]], and many M16A2s. The U.S. Air Force mostly uses M4 and GAU-5 carbines for security squadrons and M16A2s for non-security personnel. The U.S. Navy decided to retain the M16A2 and M16A3 for its units that use rifles like the U.S. Navy [[Seabees]].{{Citation needed|date=November 2009}} The U.S. Army and Marine Corps have largely relegated the M16A2 to non-combat roles, choosing instead the M16A4 and M4. Further, the M16 never entirely replaced the M14 in all roles, which continues to be used in a number of niche applications throughout the Armed Forces, especially with the U.S. Navy.

Replacement of the M16 family has been proposed at various points, and its longevity is in part due to a series of failures in projects meant to replace it, driven largely by the requirement for a significant improvement. Immediately after the introduction of the M16, the Marine Corps sought to adopt the [[Stoner 63]]{{Citation needed|date=December 2010}}. Although they found it superior in most ways, it was still at an early stage of development; the Marines chose the technically inferior but mature M16. The [[Advanced Combat Rifle]] program in the 1980s produced weapons that were superior in some ways, but none improved upon the M16 series enough to replace it. It was also potentially going to be replaced by the SABR, from the [[Objective Individual Combat Weapon program|OICW]] project. The weapon system originally planned by the OICW project was put on hold around the turn of century, in favor of a simpler new 5.56&nbsp;mm rifle project that offered less far-reaching improvements. The resulting [[XM8 rifle]] was also intended as a potential replacement for the M16 family.{{Citation needed|date=December 2010}} However, this program too ran into problems around 2004–05, and was put on hold in favor of an open competition for what became known as the OICW Increment 1. (Increment 2 is the standalone [[XM25 Individual Airburst Weapon System]], and Increment 3 is the [[XM29 OICW]], a weapon that combined the earlier two increments.) This competition was subsequently put on hold in the summer of 2005 to take into account input from other services, and on October 31, 2005, the competition was canceled.

A partial replacement for the M16 rifle is the SOF Combat Assault Rifle ([[FN SCAR|SCAR]]), designated Mk 16. The 5.56x45 Mk 16 emerged as the winner of a [[USSOCOM]] competition to find a new rifle for Special Operations Forces in 2003. Most of the SCAR's basic controls (pistol grip, magazine release, selector lever, and bolt release) share the same location and function as on the M16 and M4 they are supplementing.

Since the cancellation of the XM8 program, and into 2008, the [[LSAT rifle]] program has been pursued for the next generation of U.S. [[small arms]]. The program has already produced practical results and is currently projected to provide the next U.S. military rifle.<ref name="NRAmerican LSAT article">{{cite web|url=http://www.nrapublications.org/TAR/LSAT.asp |title=LSAT The Future of Small Arms Now? |work=American Rifleman |publisher=[[National Rifle Association]] |first=Robert |last=Bruce |date= |accessdate=2008-09-08}}</ref> Development of the LSAT rifle began in 2008.<ref name="NRAmerican LSAT article" />

Several companies have been working on and creating potential candidates for the U.S. Army's next primary weapon. The [[Heckler & Koch HK416]] has been in use by [[Delta Force]] since 2004. The HK416 is offered as a conversion kit that can [[retrofit]] current M4 carbines. The HK416 recently won a testing competition for the US Marine Corps [[M27 Infantry Automatic Rifle|Infantry Automatic Rifle]] program and entered final testing as the [[M27 Infantry Automatic Rifle|M27]] in summer 2010.<ref name="M27">{{cite web|url=http://www.marinecorpstimes.com/news/2010/07/marine_IAR_070110w/|title=Conway eyes additional testing for auto-rifle|last=Lamothe|first=Dan|date=July 2, 2010|publisher=Marine Corps Times|accessdate=2 July 2010}}</ref> The HK416 is also one of several M4 designs on the front competitors of the Army's [[Individual Carbine]] competition.<ref name="ICC">{{cite web|url=http://www.dtic.mil/ndia/2010armament/TuesdayLandmarkBTamilio.pdf|title=Project Manager Soldier Weapons Briefing for NDIA|last=Fuller|first=BG Peter N.|coauthors=COL Douglas A. Tamilio|date=18 MAY 2010|work=[[PEO Soldier]]|publisher=United States Army|accessdate=28 October 2010}}</ref> The H&K's design replaces the direct impingement gas system with a newer piston design. The reason to build a new M4 is to produce a new more reliable carbine for US troops in a few years.<ref name="ICC"/> However in November 2011 leaders of the US Marine Corps announced they will stay with current M4 Carbines and M16A4s and not adopt a ICC competition winner. The USMC is considering upgrading the M16A4.<ref>{{cite web|url=http://www.military.com/news/article/marines-wont-follow-armys-lead-on-new-carbine.html?col=1186032325324 |title=Marines Won't Follow Army's Lead on new Carbine |publisher=Military.com |date=2011-11-17 |accessdate=2012-02-18}}</ref>

During the late 1990s and early years of the 2000s (decade) the IMI developed the [[IMI Tavor TAR-21]] which has supplemented the M16s and M4s in service with the Israeli Defense Force.

The M4 carbine will eventually replace the M16 rifle in most combat units in the U.S. Army.<ref name="SmallArmsIndividual" />

===Gas Piston===
Complicating the Army search for higher reliability in the M4 is a number of observations of M4 gas piston alternatives that suffer unintended design problems. The first is that many of the gas piston modifications for the M4 isolate the piston so that piston jams or related malfunction require the entire weapon be disassembled, such disassembly cannot be performed by the end user and requires a qualified armorer to perform out of field, whereas any malfunction with the direct-impingement system can be fixed by the end user in field. The second is that gas piston alternatives use an off-axis operation of the piston that can introduce carrier tilt, whereby the bolt carrier fails to enter the buffer tube at a straight angle resulting in part wearing. The third is that the use of a sound suppressor results in hot gases entering the chamber, regardless of a direct-gas impingement or gas piston design choice.<ref>{{cite web|url=http://images.military.com/pix/defensetech/cna_m4_study_d0015259_a2.pdf |title=15259frcov.fm |format=PDF |date= |accessdate=2010-08-30}}</ref><ref name="Direct Impingement Myth">{{cite web|url=http://www.defensereview.com/the-big-m4-myth-fouling-caused-by-the-direct-impingement-gas-system-makes-the-m4-unreliable/ |title=The Big M4 Myth: "Fouling caused by the direct impingement gas system makes the M4/M4A1 Carbine unreliable." |publisher=[[Defense Review]] |accessdate=2011-07-27 |date=2010-03-19 |author=Mike Pannone}}</ref>

==See also==
{{Portal|Military of the United States}}
*[[Adaptive Combat Rifle]]
*[[AR-15 variants]] – list of all AR-15 and M16 variants
*[[Colt 9mm SMG]]
*[[Comparison of the AK-47 and M16]]
*[[Daewoo K2]], [[Republic of Korea Armed Forces]] (South Korea) assault rifle
*[[List of individual weapons of the U.S. armed forces]]
*[[M203 grenade launcher|M203 40 mm grenade launcher]]
*[[MSBS Radon]]
*[[Norinco CQ]], M16 clone developed by [[China]]
*[[Robinson Arms XCR]]
*[[T65 assault rifle]], AR-15 variant developed by [[Republic of China Army|ROC Army]]
*[[Winchester LMR]]

==Notes==
{{Reflist|colwidth=30em}}

==References==
{{Refbegin}}
*Modern Warfare, Published by Mark Dartford, Marshall Cavendish (London) 1985
*Afonso, Aniceto and Gomes, Carlos de Matos, ''Guerra Colonial'' (2000), ISBN 9724611922
*{{Cite book|first=Edward Clinton |last=Ezell |year=1984 |title=The Great Rifle Controversy: Search for the Ultimate Infantry Weapon from World War II Through Vietnam and Beyond |location=[[Harrisburg, Pennsylvania]] |publisher=Halsted Press |isbn=9780811707091}}
*{{Cite book|first=David R. |last=Hughes |year=1990 |title=The History and Development of the M16 Rifle and its Cartridge |location=[[Oceanside, California]] |publisher=Armory Publications|isbn=0962609609}}
*Hutton, Robert, ''The .223'', Guns & Ammo Annual Edition, 1971.
* McNaugher, Thomas L. "Marksmanship, Mcnamara and the M16 Rifle: Organisations, Analysis and Weapons Acquisition", http://www.rand.org/pubs/papers/P6306/
*{{Citation |last=M16 Rifle Review Panel |title=Report of the M16 Rifle Review Panel |date=1 June 1968 |url=http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA953110 |id=ADA953110 |publisher=Chief of Staff U.S. Army |doi= }}
*Pikula, Sam (Major), ''The ArmaLite AR-10'', 1998
*Rose, Alexander. ''American Rifle-A Biography.'' 2008; Bantam Dell Publishing. ISBN 978-0-553-80517-8.
*Stevens, R. Blake and Edward C. Ezell. (1994). ''The Black Rifle: M16 Retrospective'', Ontario: Collector Grade Publications.
*Urdang, Laurence, Editor in Chief. ''The Random House Dictionary of the English Language.'' 1969; Random House/New York.
{{Refend}}

==External links==
{{Commons and category|M16|M16 rifle}}
*[http://www.colt.com/mil/M16.asp Colt Manufacturing: The M16A4 Rifle]
*[http://peosoldier.army.mil/factsheets/SW_IW_M16.pdf PEO Soldier M16 fact sheet]
*[http://www.ar15.com AR15.com, the largest M-16/AR-15 Resource on the Web]
*[http://www.thegunzone.com/556dw.html The Gun Zone: A 5.56 mm Timeline]
*[http://www.rawles.to/AR-15_M16_Magazine_FAQ.html The AR-15/M16 Magazine FAQ]
*[http://www.nazarian.no/images/wep/504_FM_23-9_M16.pdf Combat Training with the M16 Manual] ([[PDF]])
*[http://www.globalsecurity.org/military/library/policy/army/fm/3-22-9/index.html Rifle Marksmanship M16A1, M16A2/3, M16A4 and M4 Carbine (Army Field Manual)]
* {{Internet Archive short film|id=AR10_Promotion|name="The Armalite AR-10"}}
* {{Internet Archive|id=ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p|name="Army Technical Manual (for M16 rifle) - TM9-1005-249-23P"}}
* {{Internet Archive|id=DaPam750-30|name="DA Pam 750-30 1969 US Army comic book for maintenance of the M16A1 rifle"}}
* {{Internet Archive|id=OperatorsManualForM16M16a1|name="Operator's Manual for Rifle, 5.56 mm, M16; Rifle 5.56 mm, M16A1"}}
* {{Internet Archive short film|id=Rifle556mmXM16E1OperationandCycleofFunctioningTF93663|name="Rifle 5.56mm, XM16E1, Operation and Cycle of Functioning TF9-3663 (1966)"}}
* {{Internet Archive short film|id=gov.dod.dimoc.28805|name="Rifle, M16A1 - Part II - Field Expedients (July 1, 1968)"}}
* {{Internet Archive short film|id=gov.archives.arc.36901|name="Fundamentals of Rifle Marksmanship (1971)"}}
* {{Internet Archive short film|id=gov.ntis.ava21011vnb1|name="Fundamentals of Rifle Marksmanship (1999)"}}
*[http://www.ar15.com/content/manuals/TM9-1005-319-10.pdf Operator's Manual for Rifle, 5.56 mm, M16A2; Rifle 5.56 mm, M16A3; Rifle, 5.56 mm, M16A4; Carbine, 5.56 mm, M4; Carbine, 5.56 mm, M4A1]
*[http://www.bimbel.de/artikel/artikel-25.html M16 in parts] (German)
*[http://discovermilitary.com/weapons/m16-rifle/ M16 Assault Rifle Description]

{{ModernUKInfWeaponsNav}}
{{ModernUSInfWeaponsNav}}
{{AR-15 variants}}
{{USAF Weapons}}

{{DEFAULTSORT:M16 Rifle}}
[[Category:5.56 mm firearms]]
[[Category:Assault rifles]]
[[Category:Infantry weapons of the Cold War]]
[[Category:Cold War rifles]]
[[Category:Colt's Manufacturing Company]]
[[Category:Rifles of the United States]]
[[Category:Weapons of the Vietnam War]]
[[Category:United States Coast Guard weapons]]
[[Category:United States Marine Corps equipment]]
[[Category:Vietnam War infantry weapons of Australia]]

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Revision as of 19:35, 16 April 2012

dirties need to shower and learn to catch gar fish

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