It really depends on how much you want to spend. At minimum I would recommend a .25. Airforce has some affordable Big Bores if your looking for something that shoots slugs. The .457 Texan is probably a great place to start. I would do some research, videos etc,and find something that has good accuracy to minimum of 100 yards. I would recommend staying away from "pellet" guns as they really don't have the power to reach out and dispatch easily.