The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, IL to exploit the accuracy advantages of the .223 Remington commercial chambering without pressure problems or compromising the functional reliability when using the high velocity 5.56x45mm NATO militaryammunition. It is used by many rifle manufacturers who sell "National Match" configuration AR-15rifles, barrels, and upper receivers. The .223 Wylde achieves better accuracy by having a chamber throat that is tighter than 5.56x45mm but will still function reliably with military 5.56 ammunition as the case dimensions are the same. In short, it will give you the accuracy of a real SAAMI when using the good ammo, but also allow you to use cheap surplus ball ammo safely. Please Google .223 Wylde if you are unfamiliar with this chamber. It is truly the best of both .223 and 5.56 chambers.