I know a big caliber handgun is gonna make ya feel all warm and fuzzy inside, but if you really want to REALISTICALLY stop a bear attack leave the handgun in the truck (or at least don't rely on it as your primary or ONLY defense) and get a can of "Bear spray".....not the little Yogi and BooBoo sized can.....they make one about the size of a can of hairspray.
Keep it in easy reach on your belt and know how to use it......IMO the only real chance you have with any handgun on a P'd off Grizzy that REALLY wants you dead ,is when its alredy standing on your neck and you are lucky enough to get the gun into its open mouth or under its chin and touch one off.
Everyone seems to think that they could down a charging Grizzly with the right gun.....99.9% of these people probably have zero chance. Of the other .1% that might pull it off.....probably half of them would just be lucky.
If you don't want it to get that far use the industrial sized can of pepper spray. Also with pepper spray.....you don't have to worry about "Shoot Don't shoot" repercussions.