what, 20 gauge equals .62 caliber, i hear of guys on the traditional muzzleloading forum killing critters bigger than that with a .62 cal lead round ball out of their smoothbore muzzleloaders and you are talking about using slugs which are have much better penetration than a round ball. You will have plenty of gun for bear, hell i was planning on using my .54 cal lyman great plains rifle with patched round ball for bear in a couple of years. Use the 20 gauge with confidence!!!!!