I was just thinking that myself. For instance, using 223 ammo in a 556 gun, apparently can't or shouldn't be done because the internet says so! Even though it has been done for many many years.
I think they got it backwards, 223 is ok to use in a 5.56, but 5.56 ammo in a 223 can develop dangerously high pressures.
NRA Lifetime Member Since 1999
"I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason