A .223 will kill deer if A]you can shoot B]know your game anatomy C] know your range limitations.With the Ruger Mini-14 the rifling twist is 1-10 or maybe faster now so you can use 60gr+ bullets.I've shot several deer with .223's and my dad with a .222 all deer dead one shot out to 150 yards.And three black bears one shot each.Again Canadian Inuit have been shooting walrus,caribou,seals,muskox and polar bear with .22 Hornets and 222's for decades now.Old news ,I'm afraid....................Harold