This is an interesting and somewhat timeless subject. I believe it is generally understood that there is no "dimensional" difference between 5.56mm and.223 Rem ammunition. However it is also said that the military 5.56mm cartridge is loaded "hotter" than the commercial .223 Rem. I can't say much about factory loaded .223 Rem as I haven't used any in many years. I can say that my reloaded ".223" is at least as "hot" as the military M193 (3250 fps mv) or M855 (3050 fps mv) and may be a bit faster with lighter bullets. As far as I know the military doesn't load any bullet below 55 grains, though they do go a bit more on the heavy side. As far as 5.56mm ammo destroying a rifle chambered for .223 Rem, maybe, but I'd like to see some evidence of that happening. Provided of course the rifle is of decent quality. I can only imagine how many tons of Lake City ammo has gone down the pipe of .223 rifles without incident. Now, does that mean destruction can't happen? No, anything is possible. Also, I believe the overall length (OAL) of military ammo is pretty much a fixed dimension regardless of the bullet type and is well short of the rifling in either type of chamber. In any case, you can't go wrong using ammo that matches the design of the rifle you are using it in. I have been busy the past few days turning several hundred Lake City 5.56 brass into .223 Rem. Now we will have to put it in my Olympic AR and turn it back into 5.56. Gerry
