I've shot quite a few deer with just a .22LR. All head shots, all dropped in their tracks. I personally seen a deer dropped in it's tracks with 6 shot from a 20 gauge. I've also shot a few with the new core loct .12 gauge remingtom sabots slugs(385 grain?) that ran well over 100 yards with a good vital shot. I think it all comes down to bullet choice. A fragmenting or rapidly expanding 5.56 will do as much damage as those Rem sabots 8 times their size that don't expand at all and pass right through.(actually, one round killed and completely passed through two deer, complete waste of energy). If the ranges are under 100 yards like you said, a good fragmenting FMJ would be fine, but for much longer distances, I'd recommend something more along the lines of a winchester moly ballistic tip. I would not hesitate to use my AR on deer, and wouldn't worry about head or neck shots either, and would also not hessitate for ranges out to 300 yards(with good optics). Shoot for the lungs/heart and you'll be fine. Bowhunters should prove to everyone that it doesn't take a bazooka to kill a deer as it's a fair bet almost any 5.56 round will cause more tissue disruption and subsequent bleed out than an arrow. Place a pellet rifle in the right area and you'll drop almost anything. Unfortuanately for me, OHIO rules dictate shotgun slugs only, so I have to break out the Benelli SBE.