Do a search on Senior Member Kieth Rogan, of Kodiak, Alaska. He got mauled a couple of years back by a big brownie, and is lucky to be alive. As such, he's made something of a study of what it takes to survive a bear attack. Check out his "Bear Maulings" website; fascinating reading.
He notes that most people assume that the brain pan is MUCH, MUCH higher up in the bear's head than it really is. This is why you hear about bullets "bouncing off" the skull of a big bear. Most likely, the bullets are actually penetrating, but are passing through a large sinus area in the skull that is nothing but air and bone. This ticks bruins off, and is deteritous to human-bear-interactions.
To hit the brain, aim for the spot directly behind the eyes. Don't aim for an individual eyehole-- just aim for the spot dead-center between them. This gives you your highest percentage shot of hitting the brain, and, according to Kieth's website, the Alaskan State troopers determined by experimentation on dead bear skulls that even the lowly .38 Special can penetrate the skull there.
Other than a brain shot, don't EVER try to shoot a bear with a pistol. You won't improve your situation, any.
[This message has been edited by Long Path (edited February 25, 2000).]