For polar bears of "Alaskan Brown Bears" (Kodiak), the preferred weapon is belt-fed.
Actually, he probably would have been OK if he had soft-point ammo.
There's an outfitter in Russia in the neighborhood of the Kamchatka penninsula who advertises bear hunts, where the object of the hunt is the twin brother of the Kodiak bears, and he specifies the .30-'06 as the minimum cartridge.
RPG, if you can get one!
I hunt polar bear from a safe distance employing global warming as my weapon of choice....