I gotta disagree with H&H. I missed the Sopranos episode, but even assuming we're talking about an SKS or AK or something with a bunch of semi-auto rounds, this just doesn't strike me as a good choice. Black bears are a whole lot smaller than their brown cousins, but they also seem to be less predictable, and some of them are remarkably big. I've been within 100 yards of blackies at least half a dozen times, and within 10-feet of an enormous one (in northern Saskatchewan) once.
The bottom line is that these guys scare me, and while I have no doubt a few rounds (or maybe even one well-placed shot) of 7.62x39 would kill them, I'm just not sure it would do the job quickly enough, especially if the bear surprised you. This is just my opinion, obviously, but I do a lot of camping in black bear country, and I do fear the critters, but it wouldn't even cross my mind to bring a 7.62x39 for protection, though I realize the selection may, and I repeat may, be different for hunting. I've never hunted the blackies, but when in their country I bring a .45-70 if possible, or at least a .44 magnum when it's not.
Then again, I stocked up for Y2K, so maybe I'm just paranoid. But I'd encourage you to not underestimate the black bears.