I bet when they switch production over from m193 federal to .223 American eagle at the factory its a matter of switching the packaging.
I am also willing to bet the cases are the same dimensional sans headstamp.
This 5.56 vs .223 argument is silly. Someone please post a link or proof of 5.56mm damaging a .223 rifle.
The 556 has more recoil than the 223. I guarantee that. I'd only shot 223 for a while and then got some 556 and noticed it right away.