The .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 and will give a reliable check of ammunition used in rifles chambered for either the .223 Remington SAAMI specifications or the 5.56 NATO specification. SEE BARRELS IN WYLDE CHAMBER

The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, IL to exploit the accuracy advantages of the .223 Remington chambering without pressure problems or compromising the functional reliability of (semi) automatic weapons like the AR-15 family when using 5.56×45mm NATO military ammunition.[2] Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the sport of Highpower Rifle Competition very well and is one of the preferred chambers for that use. The Wylde chamber is used by a few National rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.

AR-15 manufacturers incorporate the use of the Wylde chamber. Designed by and named after Bill Wylde, this chambering was designed to accurately shoot the military ball ammo of the day while still feeding reliably. Coincidentally, it shoots the longer 80 gr bullets commonly used in the sport of Highpower Rifle Competition very well and is one of the preferred chambers for that use. While the Wylde chamber allows for optimal seating depth of 80 grain bullets over .223 Remington and 5.56 NATO, it is capable of accepting both ammunition types. The Wylde chamber is used by a few manufacturers who sell "National Match" configuration AR-15 rifle, barrels, and upper receivers. The type of chamber, manufacturer, and rifling twist in inches is typically found stamped into the barrel in front of the front sight assembly.

Wylde changed the NATO reamer's overly-large freebore section, narrowing it to 0.2240", which helps guide bullets straight into the rifling. The leade angle is 1 degree, 13 minutes per side, and the throat allows 80 gr. Sierra MatchKings to be seated out to about 2.465" to touch the rifling. It is one of the longer-throated custom match reamers. If you want absolutely top accuracy, you may benefit from a relatively blunt bullet (e.g., the Sierra #1390 55 gr. HPBT) & also by seating bullets out past mag length