Nice cut and paste job, but what you're really comparing there is the difference between cored (steel or carbide) ammo and non-cored ammo as opposed to the difference between the .223 Remington and the 5.56 NATO Round. The main difference between the two is case pressure, and has little to do with the barrel and everything to do with the chamber. You can get into discussions between Berdan and Boxer primed, corrosive or non-corrosive powder, etc., but your point is moot. Commercially available (and even military surplus) 5.56 ammunition will cause no ill effects to weapon chambered for it. By the way The AR (as designed by Stoner for Armalite) was DESIGNED SPECIFICALLY AROUND THE 5.56 NATO Round. That's right genius, the round came BEFORE the rifle, and the rifle was designed to fire that round.