Lots and lots of stories about a .22 being plenty of kill.
I just have to point out one I saw where it, unfortunately, wasn't.
It was on a nature show last night. Two men, one a guide, were out walking. A polar bear approached making aggressive moves. The guide fired a warning shot, the bear wasn't scared off, the guide shot the bear multiple times, got hit by the bear. The second man managed to get the revolver. The show mentioned 'he fumbled with it', given the number of shots fired I could only think that he was trying to reload it, a revolver just fired shouldn't be difficult to fire again as long as it's loaded.
Anyways, he also shot the bear an unknown number of times more, then the bear hit him once(nonfatally), then he staggered away. It wasn't mentioned until after that that the revolver was a .22, and the gun pictured in the reenactment looked a lot more like a long barrel .357.
They tracked down the bear and killed it with a HP rifle, found that the bullets didn't penetrate the fat layer.