A short barrelled pump shotgun is out of the question? If you need to defend yourself against a bear then that means he's already running at you. Your target is bouncing around not really giving you much to shoot at.
They make bear loads that are enough. But shot placement is critical. As I said, he's already running at you and that's a tough shot to make with a handgun.
Especially if you're crappin' in your drawers.