My opinion and take it for what you will. There ain't enough difference to matter. Don't do it now because I shoot my on reloads, but I have shot 5.56 in a .223 marked rifle and no issues. Taken to an extreme with high pressure 5.56 shot in a weak chambered .223 there might could be an issue. I have bought .223 that measured exactly the same as some once fired .mil brass. Held exactly the same amount of water too. Maybe years ago there was a bigger difference I don't know.


"In time of war, send me all the Alabamians you can get, but in time of peace, for Lord's sake, send them to somebody else." General Edward H. Plummer

"Blessed are those who, in the face of death, think only about the front sight." Jeff Cooper