# 2 lead is absolute minimum size, BB or #4 buck are much better. I've killed coyotes with #6, #5, #4, but smaller shot than #2 will not always penetrate. Hevi shot does not load bismuth, they load hevi shot! I'd still stick with #2 minimum in that pellet material. Steel pellets would need to be pretty big, F or T before I'd consider using it.