It is quite possible a load of buckshot at 10feet would stop the bear - however penetration would be VERY iffy, and a hardened & solid projectile - actually 12 bore would work.

I'd take a well loaded 12 bore over any rifle in a charging bear situation. By well loaded, that means hardened round balls at about 1,500fps to 2,000fps. A pump would be much better than any other action, for me.

Factory slugs are too soft in my opinion, thus round balls would rule.

Ed Huble's 3" 12 bore loads using a hardened 500gr. .58 slug in a sabot at about 2,000fps or 2,200fps would also be more than sufficient, from a rifle bore. YOu want straight line penetration, not a bone caused deflection due to no rotational stability from a smoothbore.

Problem with the shotgun with round balls, if smooth, you'd have to wait until the bear was much closer for the shot - of course, that would make it more interesting & a better story for 'the campfire'.