I used to think that if I were being charged by a bear, I would most like to carry my 338 win mag. However, I think now I would choose my 12 gauge pump loaded with the max number of shells the gun would allow.
Check out this site:
http://www.loadammo.com/Topics/July02.htmIt helps you figure the "knock down" power of big slow moving bullets much better than using the ft/lbs method. For these purposes, the diameter of a 12 gauge is roughly 0.75 inches.