The .223 Wylde is a hybrid .223/5.56 chamber designed by Bill Wylde to yield the accuracy advantages of the match .223 Remington commercial chambering, but without pressure or reliability failures when using high velocity 5.56 NATO spec ammunition. The .223 Wylde achieves better accuracy by having a chamber throat that is tighter than 5.56, but will still function reliably with military 5.56 ammunition because the case dimensions are the same. These facts lead to the .223 Wylde having superior target and varmint accuracy, a compatibility with all .223 and 5.56 NATO ammunitions, and being a top choice for competition shooters.
Bill Wylde of Greenup, Illinois, compared the two cartridges and changed the chamber of the rifle's barrel to a specification called the .223 Wylde chamber. The chamber is made with the external dimensions and lead angle found in the military 5.56×45mm NATO cartridge and the 0.2240 inch freebore diameter 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.
While the .223 Remington and 5.56×45mm NATO chambers have slightly different dimension, the cartridges are identical in exterior dimension. The chamber dimension differences are often confused with the cartridge dimensions, and it is often erroneously thought that the cartridges have different dimensions. However, the cartridges are loaded to different pressure levels (55,000 psi vs 62,000 psi), with the 5.56 NATO being greater. The .223 Wylde chamber allows the use of both pressure levels safely, while also increasing accuracy potential across the range of potential bullet selections.
Wylde's hybrid chamber was designed to exploit the accuracy advantages of the .223 Remington chambering without problems concerning over pressure or compromising the functional reliability of semi-automatic firearms like the AR-15 family of rifles when using 5.56×45mm NATO military ammunition. Coincidentally, it can shoot the relatively long and heavy 80-grain (5.18 g) bullets commonly used in Sport Rifle Competitions very well, and is one of the preferred chambers for that task. The .223 Wylde chamber is used by rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels and upper receivers.
