I love bear gun threads.
Why not get a .50 Barrett and cut it down to a pistol grip and a 4" barrel? After all, people are already recommending guns too heavy to practically carry for significant distances in a manner conducive to getting into action in the split seconds of a bear charge...and in cartridges/small guns which would be impossible to get an accurate second or third shot off. Might as well go all the way and impress your friends.
The fact remains, all that will stop a bear charge is a shot to the CNS...put one in the vitals you would shoot into hunting and the bear will die, likely after you are already dead. And a 44Mag, a 41Mag, and perhaps even a 357Mag with the right bullets will be equally able to penetrate the CNS....and much more controllable to get in a few quick follow-up shots to increase your likelihood of success.