You know what they say about having a handgun in bear country...
Be sure to file the front sights off so it won't hurt so much when the bear takes it and shoves it up your ass ;-)
With a .500 S&W you are throwing more lead and at a faster speed than the original .45-.70 black powder rifles did. Not that I ever want to play bet your life with a bear, I am pretty sure that would stop a black bear. Grizzlies? Well, at least you would have a fighting chance.