An acquaintance of mine, who used to be a backcountry outfitter in a SW Montana wilderness, was attacked by a grizzly bear during a guided trip. Both his client and himself were mauled quite severely. While the grizzly was--quite literally--chewing on the girl's face, my acquaintance was able to put one .270 round into the bear's back. The bear then turned on him and began chewing on his legs. This, however,left his arms free to remove a .44 magnum revolver from his holster. The bear took all six rounds to the head and neck but was still able to run off for over a mile before it finally expired.
A .270 round in the midsection and six .44 magnum rounds to the head and neck before the grizzly ran off. That's what it took. Both his client and my acquaintance survived. She has massive scars where reconstructive surgery repaired her jaw and oculars and plastic surgery repaired her soft tissue. He is missing muscle tissue from his calves, scars running from his mid-thighs to his ankles on both legs, and has a prosthetic knee cap on his left leg.
No, I do not know what brand revolver or load the gentleman was using.
Steven