[Jeff Higgins]

If you are stuck with a shotgun, like in a shotgun only hunting area, I would follow Jeff's advice. That said, I'm no fan of the shotgun for big game hunting and I'm even less of a fan of them for defense against bears.

Shotguns lack penetration. Especially buckshot, but Jeff already ruled that out, and I agree. Slugs are not much better, though. They work well enough on broadside lung shots on deer and smallish black bear, but they lack the penetration needed to make it all the way through even that light resistance most of the time. Try to break a shoulder with one and often that is where they will stop, leaving a non-fatal, but very nasty wound. At least not immediately fatal.

So, what does this have to do with defending one's self against a bear? Well, assuming you even have time to react (because you see him coming), you don't get to take that broadside lung shot. He will be facing you. You will be looking to penetrate very substantial muscle and/or bone to get into the chest cavity, or one one hell of a thick skull that is laying at quite an angle. A slug will not penetrate either.

You are far better off with a light, fast handling carbine. Even the lowly thutty thutty will out-perform the mighty 12 gauge under these circumstances. Up the ante to something like Marlin's .45-70 Guide gun, and you will have some serious bear medicine in a very small, fast handling package - smaller and quicker than even a "combat" shotgun, and carrying one hell of a lot more "stopping power".