I have killed tons of deer with a 223Rem or 5.56X45. I believe that the "secret" is . . . fast twist + speed + well made bullet. I prefer the Barnes 55gr TSX. Put it on the shoulder,hit bone going in.
Does a fine job.
Down here quite a few people hunt with the 223/5.56. Single shots,bolt guns,AR's . . . they use them all.
SHOT PLACEMENT is #1 . . . then ^^^^ above. --- SAWMAN