.223 Remington

**.223 Remington** is the commercial civilian version of 5.56x45mm NATO and predates the military cartridge. The two are very nearly interchangeable but are not identical: 5.56 runs at slightly higher pressure in slightly looser chambers. Practically: a rifle stamped **.223 Rem** should only shoot .223. A rifle stamped **5.56 NATO** can shoot both. A rifle stamped **.223 Wylde** is a hybrid chamber designed for both, and it is the enthusiast choice on precision AR builds. For most new AR buyers the distinction is academic — nearly every modern AR-15 is chambered for both — but it matters for older rifles, target varmint rifles, and anyone developing loads near maximum pressure.