I actually have to agree with Lonnie on the .243 is a mainly a varmint gun. I know it's used a LOT to kill deer, and for women and kids to hunt with because it has no recoil, and it shoots fast and flat... But, that doesn't change what it is. You can kill a deer with a .22LR, but was it honestly designed for that, and does it really make it the best tool for the job? Of course not. Personally, I wouldn't go hunting for deer with anything less than a 1/4-bore. I've shot deer with a .22-250, and they've dropped, but they were all within 100-150 yards. I never pushed my luck with it. A .257 Roberts would be about the smallest bullet diameter that I'd walk into the woods to hunt deer with, based on my experiences and personal preferences.