Does anyone remember the Beltway sniper?
They used an AR in 5.56. They killed people far more often than injuring them. The round is deadly against people but using the long heavy for caliber bullets with a really fast spin results in a .223 sized hole. They will really penetrate but that is also the problem. They penetrate too easily.
My same recollection. The 5.56 round was smaller but tended to “rotate” and “disintegrate” once it entered the target, causing an astonishing amount of internal “soft tissue” damage to the target. I believe I read at one point that the 5.56 round was actually being touted as a round that caused “excessive” damage to a target due to the way it acted once it entered said “soft” target.