i will beusing my AR this coming deer season (hopefully ) in 5.56 NATO (.223)
I've killed a couple of deer with mine. It takes approprate bullet selection. I decided I was gonna stick with premium bullets, though I've read quite a few people use cheapers ones on Head and neck shots. Match and frangible bullets are not gonna cut the mustard. Quite a few good hunting bullets out there. This is where reloading really gives you a benefit. Texas Deer aren't that hard to kill.
I'd get at least a 1 in 8 twist, so as to not limit you weight (length I know). I like the heavier bullets for hunting.
I used 70 grain Barns TSX and hey worked great. both animals didn't go very far.