I've used buckshot on deer in states where it was legal, in thick stuff like you were talking about, and had I not had a slug chambered right afterwards I would have lost the deer. That was from a frontal chest shot at 15 yards. I'd have to say you can't go wrong if you use your 20 gauge slug gun. It has the stuff to take down both of those animals and they are a great brush gun. That I use anyways.