Stephen Herrero wrote a great book about bear attacks, how to avoid them, and what to do in the event of one. He has studied bear behaviour and specific attacks and provides case studies for different attack scenarios. I think everyone recreating in bear country should read it. The book goes into great detail for both black bear attacks and grizzly attacks.
He has a section on defense where he analyzes firearms. It's been awhile since I read it (and my copy is continually out on loan!) but here's some of what I remember. He prefers large caliber rifles (duh!). If I recall he also is a fan of the shotgun, but that has never been a viable option for me (honestly, who is packing a stricly defensive long gun other than a guide). He discusses pistols and bears shot with them with some contempt, both in difficulty of the shot and effectiveness of the round. In his estimation the 44 mag is the minimum effective cartridge. He says to shoot a charging bear in the shoulder. It is a larger/softer target than the skull and breaking the bones there will slow the bear down and buy time.
Herrero's book was pretty good when it first came out in the 80's, but it's outdated. I would certainly recommend it as a part of a well-rounded bear aficionado's library, but for more up-to-date information and advice, I'd recommend J. Gary Shelton's books, including
Bear Attacks: The Deadly Truth.
