I purchased the same, used from a gent before xmas too. I asked him the same question, as despite the barrel being stamped 223/5.56 I wanted his opinion on how it handled personally on the different kinds of ammo. It eats everything and no difference in FTF/FTE, I was told. If there is a moderate accuracy difference due to the varying chamber specs or whatever, I'm not too concerned, as this is for very short ranges anyways (10.5" barrel).