Question folks, seems like I am getting the same type controversy as with the .308 Winchester and 7.62 x 51 nato , here is the question: Is it safe to fire .223 Remington in a firearm where the barrel ( not the receiver) is marked 5.56 x 45 Nato?
100% true, the 5.56mm brass is not thicker than .223 brass.FWIW, 5.56 brass is not thicker than .223 nor is case capacity less.