Seems like you’d get a degree of bouncing around trying to shoot that rapid as well. The mechanism itself would seem to prevent that rapid of a sequence.
.223 seems like a very small round. A rifle is often used for distance shooting, and it seems it wouldn’t be all that stable since it’s so lite.
.223 is designed for anti-personnel encounters. There have been reports from soldiers in Iraq and Afghanistan of enemies taking two or three rounds of .223 and still walking or firing their weapons. The military switched to it because it meant they could carry more into battle.
As far as pure power for anti-personnel, you can’t go wrong with good-old .308. If the SHTF, I’ll be throwing .308 down the line to make sure what I hit dies or at least can’t get up.