Ironically the prevalence of AR-15s has made people underestimate the amount of power and damage that most deer hunting rifles possess. 5.56 is like the bare minimum you can get away with to reliably disable or mortally wound a human or similarly sized animal, which is why the military used it because it saves weight so soldiers can carry more of it even if they have to hike 20 miles to their objective. Most hunting rifles are serious overkill for killing their target because hunters want instant take downs, not an animal that is able to stand up and get an adrenaline boost and sprint away if even for just 15 seconds into the brush because the shot was a half inch to the left. .30_06, a common deer round and used in the M1 Garand of WWII, is just under twice the muzzle energy of 5.56.