The_Dunedan

The 5.7x28mm round is totally unsuitable for bears, although it does a nice number on humans. The Tungsten-carbide AP round is military/LE-only, and is intended to penetrate body armor, then yaw 90 degrees and fly sideways for 8-12" at most in order to avoid overpenetration while delivering a .40 wound channel. This is barely enough to get through a Grizzley's fat layer and muscles, which is much denser than the human medium the round was designed to behave in. All the 5.7 would do is piss the thing off, and possibly without even the "revenge" benefit of Yogi dying in horrible pain a week later. The only possibly workable shot would be the classic "brainer," which although it might be do-able is certainly not something you want to be limited to. 5.7x28 is for armor-wearing humans, not bears.

Edited to add: I should say that I know of at least one incident of 5.7x28mm being used to harvest a wild hog. The round's performance was described as impressive, but it was a precisely-placed headshot delivered by an expert marksman. Still, penetrating the skull of a wild hog is no mean thing out of a .221 handgun/submachinegun round. However, again, not the kind of thing I'd want to have to put my trust in if for no other reason than that the frontal brain-shot may not be the shot you get. The 5.7mm is a beautiful round within its' performance envelope, but bears just aren't in it IMO. I'd be interested to know if there've been any encounters which've featured the 5.7mm.