"If you need an AR 15 to kill a deer, you ought to stick to fishing!"---Senator Richard Durbin,

[madville]

32. You're partially correct

Yes, you can shoot .223 REM in a rifle chambered in 5.56 NATO but should NEVER shoot 5.56 NATO in a rifle chambered for .223 REM.

But most civilian AR-15’s are chambered in 5.56 NATO though so it’s safe to shoot both. Best thing to do is always check the barrel of the firearm, it will be stamped with the caliber, either 5.56 NATO or .223 REM in this case.