Personally, I would never shoot a deer with a .223, I know that there have been piles of deer killed with them, but it is much too iffy, in my opinion. If you like to hunt with you AR, why not check out some of the uppers out there and get one chambered for, say 308, 260, or even the 300 WSM, or 450 Bushmaster? The milder cartridges hedge your bet and won't pound you. The bigger ones are even better. I know that there are many who may disagree, but our game deserves a clean, humane kill, and the chances of doing this are greatly increased if you use a caliber and load suited for the job. Just my 2c!