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The term .223 Wylde describes a feature of design of a rifle barrel that can be used in any rifle that is being engineered to use 5.56x45mm NATO ammunition.
History and Rationale
In 1950 the Remington Arms company's Mike Walker designs the .222 Remington as a new intermediate power cartridge sized between the .22 Hornet and the .220 Swift. This cartridge found great acceptance among Varmint Hunters and Benchrest shooters.
In 1957 during research into development of a military .22 caliber rifle the Remington .222 Special is created. In 1959 due to there being several .222 caliber cartridges being developed the .222 Special is renamed to .223 Remington. The cartridge becomes the standard for the US Army in 1962 as M193 Cartridge.
SS109 (5.56 NATO)
In 1972 Fabrique Nationale (FN) created a new class of ammunition for NATO. Based on the .223 Remington cartridge which was being used by the US Army which had greater range and effectiveness. The first iteration of this ammunition was type designated SS109. Where .223 Remington had featured a 55 grain full metal jacket boattail which was the analogue of the US M1 .30 Caliber rifle bullet the SS109 used a 62 grain bullet which contained a steel penetrator. Due to differences in the case dimensions between the .223 Rem and 5.56 x 45mm NATO (SS109) the two cannot be used interchangeably. The .223 Rem cartridge is more accurate but the 5.56 mm NATO cartridge is more powerful and has longer range. The BIG difference though is that the pressure levels in 5.56mm NATO are higher. While the .223 Rem produces 55,000 psi chamber pressure the 5.56mm NATO produces 62,000. The US follows NATO specifications. The 55 grain projectile in US use is typed as M193. The Fabrique Nationale developed SS109 as the earlier penetrator round in 62 grain. This has been refined for better penetration per US military specification and is now designated M855. When the US adopted the NATO spec a large number of existing rifles had to be rebarreled for the faster rifle rate necessary.
Lack of Interchangeability
Some rifles are chambered for .223 Rem. They should not use 5.56mm NATO ammunition. As most rifle makers have changed to support the 5.56mm NATO specification the reduced accuracy was considered a problem. Since the .223 Wylde chambering solves the accuracy problem in rifles made for 5.56mm many rifle component makers now offer it.
Although a rifle barrel that is chambered in .223 Rem can fire 5.56mm it is not advised due to 5.56mm having higher pressure. It is also not advised due to the bullets used in SS109 (M855) family being longer and heavier. The rifling twist ratio for .223 Rem is 1 turn in 10 inches of travel (1:10). Due to the heavier and longer bullets used n SS109 (M855) family the military guns are rifled at a 1:7 ratio.
Bill Wylde's Contribution
Bill Wylde compared the two cartridges and changed the chamber of the rifle's barrel to a new specification which is called .223 Wylde.
.223 Wylde is a proprietary rifle cartridge chamber with the external dimensions and lead angle as found in the military 5.56×45mm NATO cartridge and the 0.2240 inch freebore diameter as found in the civilian SAAMI .223 Remington cartridge. Rifles with a .223 Wylde chamber will typically accept both .223 Remington and 5.56×45mm NATO ammunition. Note that while the .223 Remington and 5.56×45mm NATO chambers have slightly different dimension, the cartridges themselves are identical in dimension. The chamber dimension differences are often confused with the cartridge dimensions and so it is often erroneously thought that the cartridges have different dimensions. The cartridges are loaded to different pressure levels (with the 5.56 being greater), however. (The NATO dimensions offset the higher pressure with a longer throat - often confusing some to think the cartridge itself is longer). This chamber allows the use of both pressure levels safely while also increasing accuracy potential across the range of potential pressures.
The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, Illinois, to exploit the accuracy advantages of the .223 Remington chambering without pressure problems or compromising the functional reliability of semi-auto firearms like the AR-15 family when using 5.56×45mm NATO military ammunition. Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the Sport Rifle Competition very well and is one of the preferred chambers for that use. The Wylde chamber is used by a few rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.
AR Rifle Builders
The .223 Wylde chamber is not a caliber, it is a barrel specification. All .223 Wylde chambered rifles are capable of firing both .223 Remington and 5.56×45mm NATO ammunition. The Wylde chamber is considered a "match" quality chambering and produces accuracy levels that are comparable in both calibers.
The .223 Wylde specification is ONE of the important aspects of assembling an AR styled rifle. The other is barrel rifling twist rate. When the .223 Rem was developed initially it was designed to have a rifling twist ratio of 1 turn in 14 (1:14) inches barrel length. This was immediately changed to 1:12. Due to the longer 62 grain bullets loaded in the SS109 5.56×45mm NATO round the military rifles (such as the M249 FN Minimi) use a twist rate of 1:7. This twist rate is needed for adequate down range bullet stabilization as the SS100 series includes slightly longer and heavier bullet loadings in the SS110 and SS111 tracer rounds.
The barrels that are chambered in .223 Wylde caliber are offered in multiple twist rates. Most are built at 1:9 which is considered a good compromise if a shooter is going to use both .223 Rem and 5.56×45mm NATO. The 1:8 ratio is also available, as is the 1:7.