but 5.56MM NATO 55 Grain FMJ will work for most things.
WTH? Really? Any reported stopping issues with the .223 and pretty much any other cartridge man has devised has to do with the crappy ass solid and FMJ bullets. Clear back in the day of the .45colt everyone but the military figured out that solid pointy bullets zip right thru things doing very little damage along the way as compared to alternative bullets. .223 with good bullets = good, .223 with crappy bullets equals crappy. FMJ = crappy. Who'd a thunk it?
The .223 and the .45acp kill things in different ways. One uses speed and expanding bullets to open up wound channels the other uses weight and diameter. I doubt you could shoot enough men with carbines at SD distances to accurately figure out which is best given the load was up to the job.