Ruger AR-556 MPR 223 WYLDE Semi-Auto Rifle. 18 in barrel, 30 rd capacity, gray polymer finish

The 223 Wylde is not a cartridge but a chamber. Although case dimensions of the 223 Remington and 5.56x45mm NATO cartridge are identical, pressures are not the same, chambers are not cut the same, and the two are not fully interchangeable. 5.56x45mm NATO ammunition should not be fired in a 223 Remington chamber. 223 Remington ammunition can safely be fired in a 5.56x45mm NATO chamber--but functioning may not be perfect in all semiautomatic actions. Bill Wylde of Greenup, Illinois created a "hybrid" chamber that enables full use of both types of ammunition in the same chamber, essentially the best of all worlds because of the huge variety of both 223 and 5.56 loads on the market. — Craig Boddington