Between the .338 and .308 comparison of knockdown power, the .338 wins hands down, it's a HECK of a lot bigger case, so it's a no-brainer there...the .308 is a decent bear rifle, for smaller species, i.e. it's a good Bruin rifle, but a little light for grizz-it's been used on them with varying degrees of success for decades...the .338 is a better choice, and certainly would be my choice of the two.

The 7.62x39mm is a lot stouter than people give it credit for, but it's not a primary bear round, as mentioned above, it's slightly behind a .30-30win as far as performance goes, capable of about the same game ranges as a .243, although the energy differences are quite large...I've used one to 280yrds on whitetails over 200#, one shot drops in both cases at that distance-handload a better bullet (find a light weight .308Win bullet .311") and it's quite a handy round.