Sat in a blind saturday evening with a young feller on his first deer hunt ever. Shortly before dark a fat spike buck walked out about 50 yards away and stood there like it didn't have a care in the world. Gave him time enough to get the little Handi Rifle in .223 out the window, hammer back, and squeeze off a shot. Buck dropped in its tracks, the 60 grain Nosler Partition hit a little high, got the top part of the lungs, and bottom edge of the spine along with the decending aorta etc. About an hour earlier I had heard a shot from the location a friend was hunting with his daughter and a DPMS AR in .223, with some 62 grain soft points one shot one kill as well, then received a text/photo from another buddy with his son of a decent buck taken with the Handi Rifle in .223 and some 62 grain Fusion ammo, all one shot kills. Guess that answers the questions about a .223 Rem. Feed it good ammo made for hunting, keep the range reasonable, put the bullets where they belong and keep your knife sharp and camera charged up.