I would recommend a deer use something like a 223. Deer are fast and can run away from most threats,so their most likely to have to stay and fight if its man they are up against,becuase hes going to "reach out" with some sort of high powered rifle or with a bow. 223 is light and accurate and made for humans,so it should work very well. They also often hunt in packs,so if you wound or kill one,the others will usually stay behind to help rather than giving chase. Any of the typical 55-60gr bullets should work just fine. Its most important though for deer to get a lot of practice during the off season and keep their wits about them when in season. You cant miss fast enough to stay out of Bubbas freezer.