Ditto what most of the others said. Yes it will kill a deer with good shot placement but I would go with a larger caliber. Those little .22 caliber bullets out of a .223 are super fast but very light weight. Most factory loaded shells will come loaded with about a 55 grain bullet. Hit a little far foward and catch shoulder blade or heavy bone with a bullet that small and you are looking at a lost deer. I personally would not hunt deer with any bullet less than 100 grains in weight and that means using at least a .243.