NEWS YOU CAN USE: 5.56 NATO vs. .223 Rem.: What’s the Difference? You can shoot .223 in a 5.56, but not the other way around. “It is, and always will be, safe to shoot .223 Rem. ammunition in a chamber marked for 5.56 NATO. Commit that idea to memory, and you’ll never get in trouble. The pressures that a 5.56 NATO cartridge can generate are too high for the .223 Rem. chamber.”