6.5mm Grendel showing variety of bullets 144 gr (9.3 g) to 90 gr (5.8 g)
|Place of origin||United States|
|Designer||Bill Alexander and Janne Pohjoispää|
|Parent case||.220 Russian|
|Case type||Rimless, bottleneck|
|Bullet diameter||6.71 mm (0.264 in)|
|Neck diameter||7.44 mm (0.293 in)|
|Shoulder diameter||10.87 mm (0.428 in)|
|Base diameter||11.15 mm (0.439 in)|
|Rim diameter||11.2 mm (0.44 in)|
|Rim thickness||1.5 mm (0.059 in)|
|Case length||38.7 mm (1.52 in)|
|Overall length||57.5 mm (2.26 in)|
|Rifling twist||1 in 8" or 1 in 9"|
|Primer type||Small rifle|
|Test barrel length: 24 inches
Source(s): Alexander Arms Pressure-safe Load Data
The 6.5mm Grendel (6.5×39mm) is an intermediate cartridge designed by Arne Brennan, Bill Alexander, and Janne Pohjoispää as a low recoil, high accuracy, 200-800 yard cartridge specifically for the AR-15. It is an improved variation of the 6.5mm PPC. Since its introduction, it has proven to be a versatile design and is now expanding out into other firearms including bolt-action rifles and the Kalashnikov system.
Development and history
The 6.5mm Grendel design goal was to create an effective 200-800 yard AR-15 magazine-length cartridge for the AR-15 that surpassed the performance of the native 5.56 NATO / 223 Remington cartridge. Constrained by the length of the 5.56×45mm NATO round, the Grendel designers decided to use a shorter, larger diameter case for higher powder volume while allowing space for long, streamlined, high ballistic coefficient (BC) bullets. Firing factory loaded ammunition loaded with bullets ranging from 90 to 129 grains (5.8–8.4 g), its muzzle velocity ranges from 2,500 ft/s (760 m/s) with 129- and 130-grain (8.4 g) bullets to 2,900 ft/s (880 m/s) with 90 gr (5.8 g) bullets (similar in velocity to a 5.56 mm 77-grain (5.0 g) round).
The case head diameter of the Grendel is the same as that of the .220 Russian, the 7.62×39mm, and 6.5mm PPC cases. This diameter is larger than the 5.56×45mm NATO, thereby necessitating the use of a non-standard AR-15 bolt. The increased case diameter results in a small reduction in the capacity of standard size M16/AR-15 magazines. A Grendel magazine with the same dimensions as a STANAG 30-round 5.56 magazine will hold 26 rounds of 6.5mm ammunition.
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- 1943: The Soviets develop and adopt the 7.62×39mm M43 cartridge and begin to field it.
- Late 1950s: The .220 Russian hunting cartridge is developed, based on the military 7.62×39mm M43 design.
- 1984: Louis Palmisano and William B. Davis, PhD, develop the 6.5mm PPC from the .220 Russian for the US Shooting Team for use in bolt-action rifles in the 1986 world championships. While performance was exceptional, the US Shooting Team stays with 6mm. The 6.5mm PPC is shelved and never seen again, although Dr. Louis Palmisano believes the 6.5mm PPC could be a formidable competition cartridge with new sub-100 grain bullets.
- 1998: Arne Brennan, a competition shooter and founder of competitionshooting.com, designs and orders a 6.5 PPC reamer from JGS Tool optimized for AR-15 magazine length after conducting extensive theoretical study of multiple calibers and cartridge cases.
- 2000: Arne Brennan, after thousands of rounds of testing 6.5 PPC, compares notes with Dr Louis Palmisano (creator of the 22 and 6mm PPC cartridges).
- Early 2002: Bill Alexander, an engineer who worked for the British Ministry of Defense and designer of the .224 BOZ, .499 L-W and .50 Beowulf cartridges, begins research on developing a 6.5mm Intermediate cartridge specifically for the AR-15. Eventually the 6.5mm PPC caught his attention as it would fit his existing high strength .50 Beowulf bolt. So he machined a solid brass 6.5mm PPC dummy round. It was a cartridge that was small enough to double-stack in an AR-15 size magazine.
- July 2002: American firearms journalist David M. Fortier and Bill Alexander share ideas for a 6.5mm Intermediate cartridge. Fortier shares his idea for a 7.62×39mm based cartridge for use in the Kalashnikov system. He shelves his idea, though, when Alexander shares what he is working on for the AR-15.
- August 2002: Arne Brennan and Bill Alexander are introduced by a mutual acquaintance at Lothar Walther USA.
- January 2003: Janne Pohjoispää, an engineer working for Lapua, and Bill Alexander begin working together on designing and finalizing what would become the 6.5mm Grendel cartridge. Pohjoispää decides against basing it on the PPC as Lapua is already producing .220 Russian brass. He redesigns it using Lapua's .220 Russian case as the starting point. The two bounce ideas off each other and finalize the cartridge. The end result is noticeably different than Brennan and Alexander's original 6.5mm-PPC-based design. The new design features a relocated shoulder, increased case capacity, and a thicker neck for increased case life in auto-loading rifles.
- November 2003: Alexander Arms pays for the cartridge tooling and places an initial order for 50,000 brass cases.
- November 2003: JGS produces the first reamer for the new cartridge.
- January 2004: Alexander Arms officially introduces their new cartridge, dubbed the 6.5mm Grendel, at the SHOT Show. They introduce both a line of rifles and ammunition.
- May 2006: Independent ballistic gelatin testing completed for 90 gr (5.8 g) TNT, 120 grains (7.8 g) Norma, 120 gr (7.8 g) SMK, and 123 grains (8.0 g) SMK prototype.
- Aug 2006: Pressure safe loading data is published for AR firearms with 14.5- to 28.0-inch (370–710 mm) barrels.
- Feb 2007: Production Wolf brand ammunition becomes available. Wolf Performance Ammunition becomes a supporter of the cartridge and introduces both a 123 grain Soft Point and 120 grain Multi Purpose Tactical HPBT in their brass-cased Gold line.
- Nov 2009: Hornady teams with Alexander Arms to produce 6.5mm Grendel ammunition, cartridge cases, and dedicated projectiles. They introduce a 123 grain AMAX load, which quickly gains a reputation for excellent accuracy.
- Early 2011: Barnaul of Russia begins development of a 110 grain FMJ-BT load using steel cartridge cases. Preproduction cases are delivered for testing in the fall of 2011.
- June 2014: Production 100gr FMJ Wolf Steel Case ammunition becomes available in large quantities in the US, offering an economical factory load for the 6.5 Grendel.
Proponents assert that the Grendel is a middle ground between the 5.56×45mm NATO and the 7.62×51mm NATO. It retains greater terminal energy at extended ranges than either of these cartridges due to its higher ballistic coefficient. For example, the 123 gr (8.0 g) 6.5 Grendel has more energy and better armor penetration at 1,000 meters than the larger and heavier 147 gr (9.5 g) M80 7.62 NATO round.
While the round has impressive performance, it is not without shortfalls. In order to obtain ballistics that are superior to the 7.62×51mm cartridge, a weapon with a longer barrel and firing a heavier bullet is necessary. To achieve the same results from shorter length barrels, even heavier bullets are needed.
|Bullet velocity: 24 inch (609.6 mm) barrel|
|Bullet mass||Muzzle velocity||1,000 meter velocity|
As noted above, the Grendel case is very closely related to the .220 Russian case. In general, each additional grain of bullet weight will reduce muzzle velocity by 10 ft/s (47 m/s for each gram) and each additional inch of barrel length will increase muzzle velocity by 20 ft/s (2.4 m/s for each centimeter). Therefore, a handy rule of thumb is "one inch of barrel length equals two grains of bullet weight (1 mm → 5 mg)". Specific details are available as graphs derived from Alexander Arms' public domain load table linked below.
The cartridge developer, Bill Alexander, has been quoted as saying he was looking for a cartridge with "more legs" (i.e. longer effective range) than the .50 Beowulf so that it could be used for white tail deer hunting. The round's original marketing for military and police usage created skepticism about its suitability for hunting. Despite this, there has been critical acknowledgement that it is sufficient for CXP2 class game such as deer. Its manufacturer is more enthusiastic, saying that it has "flat trajectories and bullets well-suited to deer and varmints". It is similar to deer cartridges such as the .30-30 Winchester, .257 Roberts and .243 Winchester but is not in the same class as the .270 Winchester or the 30-06.
Army and police uses
Serbia is in process of adopting a rifle made by Zastava Arms  in 6.5 mm Grendel caliber as main armament for its armed forces. USA manufactured rifle in 6.5mm Grendel caliber will also be adopted in armament for special forces units after it passes testing in Technical Testing Center. Three types of 6.5mm Grendel ammunition produced by Prvi Partizan Uzice Serbia will be tested for use with these rifles. 
- 6mm AR: a 6.0mm version which shares Grendel's casing, but sends a (usually) lighter projectile up to 1,000 yards.
- List of AR platform calibers
- List of rifle cartridges
- Table of handgun and rifle cartridges
- "6.5mm Grendel (internet archive copy)". Alexander Arms. Archived from the original on January 9, 2012. Retrieved 2015-10-22.
- Guthrie, J (November 16, 2012). "6.5mm Grendel: The Round the Military Ought to Have". Shooting Times. Retrieved March 8, 2013.
- Lewis, Jack (2007). The Gun Digest Book of Assault Weapons. Gun Digest Books. p. 77. ISBN 978-0-89689-498-3.
- Outdoor Hub, Prototype 6.5 Grendel AK Rifle from Definitive Arms, 13 October 2015
- "Alexander Arms Announces: The 6.5 Grendel Is An Official SAAMI Cartridge "
- The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC) by Anthony G Williams
- Ehrhart, Thomas P. Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half Kilometer. pg 37-38
- Infantry Weapons Conference Report - SAdefensejournal.com, 9 January 2012
- Another 7.62mm Bullet For M-16s - Strategypage.com, 8 January 2012
- The Army’s Individual Carbine Competition: What’s Next? - SAdefensejournal.com, 24 October 2013
- Hawks, Chuck (2005), The 6.5mm Grendel, Guns and Shooting Online, retrieved January 31, 2013
- Product FAQs Q9, Alexander Arms, retrieved January 21, 2013
- Guns 'n' Ammo: Book of the AR-15, 2004, "The 6.5mm Grendel," David Fortier, p. 66.
- Special Weapons for Military & Police, Annual #27 2004, "Beyond the 5.56mm NATO," Stan Crist, p. 62-67.
- Guns 'n' Ammo: Book of the AR-15, 2005, "6.5mm Grendel and 6.8 SPC," David Fortier, p. 32-44.
- Shooting Times, February 2005, "Cooking up Loads for the 6.5mm Grendel," David Fortier, p. 52-56.
- Shooting Illustrated, September 2005, "6.5mm Grendel and Alexander Arms," J. Guthrie, p. 34-37, 67-69.
- Petersen's: Rifle Shooter, March/April 2006, "Cartridge Efficiency - Why case shape matters," M.L. McPherson, p. 22-24.
- Shooting Times, January 2007, "Other AR Chamberings," Sidebar Article, David Fortier, p. 56.
- Special Weapons, Semi-Annual #50 2007, "The Super Versatile AR," Charlie Cutshaw, p. 44-45, 80-83.
- Special Weapons, Semi-Annual #50 2007, "5.56mm NATO Alternatives," Stan Crist, p. 52-59.
- Shooting Times, March 2007, "Les Baer's 6.5mm Grendel AR Sets a New Standard," David Fortier, p. 26-32.
- Special Weapons for Military & Police #52, Spring 2007, "BETTER-IDEA 6.5mm GRENDEL," Stan Crist
- Special Weapons for Military & Police #52, Spring 2007, "New Battlefield Requirements - New Rifles and Ammo Needed," Charlie Cutshaw
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