One thing I can't see having been mentioned by anyone yet is to get a gun that fits you perfectly and you can shoot fast and accurately. The length of the barrel, weight of the gun, size of the bore, how hard it hits and how many rounds you can carry in the gun doesn't matter much if you can't shoulder it fast and hit the right spot on a charging animal at short ranges. Get a gun that fits you perfectly, have great balance, feeds flawlessly and naturally points to where you want to shoot with no adjustments needed. If you have that, any .375 or larger with bullets that penetrates well, will do. Of course larger is better, but only as long as you handle the recoil well to shoot quick accurate follow up shots. Then you need to practice a lot with it.