7.62x39 upper with Wolf HP, I've taken many a white tail with this combo. Like others have said, shot placement and bullet selection are important here with a 223.
I've shot four deer with a .223, two does and an 8 point with my AR in previous seasons and a big 8 point with a Savage .223 this season. The 8 point from this year weighed 165#. All four of these deer dropped dead in their tracks with one well placed shot each. I have been using Barnes Vortex ammo with the 55 grain Barnes TSX bullet. It's a devastating round to say the least.
Do your part and put it in the boiler room and the bullet will do its job. Deer are lost due to poor shot placement, not because of what caliber we shot it with.