A couple of months ago I was going to start a post on this subject, but praising the 38 S&W as a bear defence weapon....just to stir the pot.

If you don't believe me check with Billy the Kid. I intended to say that if a bear is on top of you and chewing on your face one shot to the brain might do the trick.
Well, here's something to chew on: I've shot a few blacks, never a griz. The first was a largish boar at 25 yds.+-, the rifle a 300 H&H with a 180 gr. Speer bullet. He was standing still on four legs, facing me directly. I hit him dead centre in the brisket, and he dropped literally spead-eagled in his tracks. Trouble was he got up just as fast as he went down and boogied off up the hill about 50 yds before giving up. The bullet penetrated right through to his fundamental orifice, destroying most everything on route.
Since that day many years ago I've shot a couple more, all hit well with powerful rifles, and only one with a broken back went down to stay without moving. Even a heart shot will not always and positively put a black down in his tracks.
Bear hunting and bear defence are NOT the same thing. Once the sucker is heading for you with serious intent you're only going to get one shot with a handgun unless he's 50 yds or more away to start.
In that case he's not really a threat yet, and a tale of defensive shooting might not wash. If he's 20 yds. away and on the run you won't have a hope in hell of getting off more than one shot, and please don't argue unless you've been there seen that. Can anyone get off two aimed shots in 1.3 seconds?
Bear hunting with a handgun (where legal) is a different kettle of fish.

Lots of experienced handgunners do it successfully, but many if not most like to have a rifle or shotgun shooter around for backup, even for blacks. Remember, if he's not charging, he'll probably run in about the same direction he was facing when hit...not look around for the source. No problem.
Dingus is dead right...no pun intended. If any make of bear is on top of you a handgun is a very good thing to have. Stick the muzzle under his throat, in his ear, or in his gaping jaws and pull the trigger. Before we arrive at that most unpleasant situation the odds are he or she will stop the charge anyway before beginning to dine on your carcass.
Unless you've further pissed him or her off by inflicting a painful wound.
While we're shooting bears: Buckshot is utterly useless at anything over point blank range, and the fabled b.s about "blinding him" is just that, fable or conjecture. The chance of one of those few pellets actually hitting even one eye is slim indeed. If you wanna blind a bear to see what happens go with 7 1/2 trap load. If you wanna kill it, go with a slug.