I get a kick out of guys dealing with Black Bears that think they have much in common with Grizzlies, it's almost like they're different animals.
Yes and no. Pounder used to say that black bears don't attack, they feed. If considering that doesn't give you pause it should. Amongst the 3 primary bear species we have in this country, problem bears tend to be sub adults. Thus a problem grizzly or polar bear might well be black bear size. The thing is that when considering suitable guns and cartridges for bear protection, one should keep in mind that defensive guns are normally used at close range.
Around here the go to gun for the majority of folks is a slug loaded 12 ga. A few of us have had carry permits where .357 and .44 magnums are generally preferred, so what rifle cartridge has similar terminal performance to a .357 handgun? The .30 Carbine comes to mind, yet few would advocate for the choice of an M-1 carbine as their primary bear gun. I once got into a discussion with a fellow on a bear defense thread who opined that an SKS was a dandy black bear gun. I'm a little embarrassed to say that I disagreed with his assessment, because properly loaded, it would be.
The key to bear defense with a firearm has a lot less to do with the gun and a lot more to do with the competence and coolness of the shooter. That doesn't mean that the choice of gun is irrelevant, since the circumstances of any potential bear conflict must be considered. For example I'm more inclined to use a shotgun near town and a rifle out on the coast, and I'm more inclined to use a scope sighted high velocity rifle if I'm bear guarding were numerous clients tend to be spread out over a wide area and an iron sighted rifle or one with a low power scope or even a shotgun if my people are nearby.
In the case of a rifle used for sheep hunting which might have to be used to defend you from a grizzly, a .30/06 is not just fine, its an excellent choice. I'd use a fragile flat shooting bullet like a 150 gr Ballistic Tip for the sheep, and have the magazine loaded with 180-200 gr Partitions. In a defensive shooting scenario, the shot will be taken before the bullet crosses the line of sight, so that fact that the rifle isn't sighted for the heavier bullet is of little concern.
In closing, I no longer like to make decisions based on chances. One day my wife and I were walking along a trail that paralleled the coast, and being low tide I suggested we cut across the tidal flats to an esker that would shorten our hike by a couple of miles. My wife replied that she didn't like the idea of busting through the thick willows that lay between us and the coast. I got a little annoyed at this and said, "That stand of willows is two mile long, what are the chances there will be a bear right where we cut through??!!" As it turned out, 100%
