If it's legal, use the heaviest bullet your rifle shoots well, and pick your shots carefully. Poachers have used the 22LR (and even shorts) to kill deer for years, The .223 should kill like lightning with properly placed shots. I'm NOT saying it's a great deer caliber, just that it can be done. A 2X4 also works, if you get close enough, but I don't recommend it. :wink:
PJ