IMO, either will kill a person with no problem! i used to think of the 223 as a pi$$ poor excuse for a rifle round, except for targets and varmints. now that i own one, and see for myself what it will do, i am quite impressed with it. if i were to be in a firefight, which would i choose? that would depend mostly on the enviroment. in my house, where distances are very short, and i may have to go around a corner or two, i would take my 45. for me, it is just quicker to get into action. if i was in an outside enviroment, where the distances were measured in yards instead of feet, the 223 would be my choice. i am still not impressed with fmj bullets, in anything. i understand the reasons the military uses them, but i like bullets that expand, unless i am trying to shoot through steel.