envonge: the .50 BMG is, generally speaking, adequate for dealing with minor threats. Excellent varmint rifle, decent for deer, getting a little iffy for bear.
Bob: The automatic revolver in .50 BMG is NOT a good choice. Compared with the Arctic Hawk .50 autoloader, it has a much slower rate of fire (3 rps versus 6 rps for the Hawk) - and no tac rail. You need all the rounds you can get.
An optimum round for anti-personnel use, proven over and over again throughout my career in the SpecOps community, is 22mm Nato - known as .86 over here. I don't recall how much muzzle energy you get, but it's in the neigborhood of 16 metric tons. If you don't need range, get 22mm RN. If you want a match-grade rifle, opt for the 22mm Spire Tip (ST). The RN goes okay in a lever rifle, while the ST can be found in the Hi-Point Anti-Materiel Carbine.
Good luck!