I know I have seen, and personally sent, multiple bullets in multiple calibers, from pistols to shotgun shells, to rifles, right through (albeit skinned) bear skulls, both black and brown, in tests of my own. That 9mm will make a hole, if he is close enough AND the shot goes where you want it to.
Most people, in my experience, decide that handguns are worthless on bears because they, for some reason, only think you would shoot at them while they are still 20-30 yards or more away.
I, for one, would not stop shooting until he has eaten both of my hands (or worse) - and if he is close enough to chew on you, then you can all but Mafia style him in the temple, eyeball, or mouth, at a distance making it awfully hard to miss.
For my two cents, pistols are not great if you want to stop the bear while he is still far enough away that you can't spit on him. But as a means of potentially saving your life at Do or Die range (close enough to leave powder burns), it's a rare handgun that CAN'T penetrate a bears skull.
