The lightest S&W revolver I know of which can be loaded with heavy enough loads for bear, is the 396 in 44 Spl., but it's REALLY light and when shot with the appropriately heavy loads, it'll be a handful. The 45 Colt MG would be a very good choice, but it's heavier. Of course, that will make it easier to shoot well.
It's really a question of what you can handle recoil-wise vs. how much you'll be carrying vs. shooting. Considering that bear attacks of people inside the parks when there was no CCW allowed was virtually nil, my guess is that, unless you do something silly mindset-wise (because now you're packing a pistol), you'll carry this gun A LOT more than you'll shoot it. I'd bet you could take 15 week-long vacations to Yellowstone and never have need to shoot it, IF you do the right things for camping in bear country. Therefore, I'd pop for the 396, or the 44 Magnum version 329. You'll shoot these at home only and probably never at the park.
My one worry about the politics of this situation is that someone will carry (legally with their CCW or not - lots of knuckleheads say, if it's good enough for a CCW holder, I'll carry there too) and then feel they don't have to hoist their food into a tree at night (bear bag) or dispose of their garbage properly, or do other things which attract bears. AND, then, instead of retreating from the bear in a safe way, decide that since they have a gun, they can "have it out" with the bear. This kind of scenario will get the CCW authorization repealed... Not saying you're that way at all. In fact, my guess is that the kind of person who congregates here is the opposite of that kind of person. This is just kind of a rant about some of the mentality I see / hear in others regarding this issue...
So, another couple points:
1. If you're carrying the gun, carry some bear mace as well. It shows you're not the kind of person who is looking for an opportunity to combat a bear, but that you'd rather discourage the bear and only use the gun as last resort.
2. Study up on the techniques to deal with a bear attack. This can be a little controversial, but the people whose opinion I respect are the ones who have had successful bear encounters. They've said that a bear is a lot like a dog in that if you run, they'll perceive you as weak and "prey" which can be chased down and eaten. Stand your ground, make noise (once you've come to the bears' attention), show no fear (that's where a gun can really help - if you feel confident of protecting yourself, you can feel more self-assured to stand your ground and retreat properly from a bear), use the bear mace, and after there's been a "stand-off" back away slowly -- without turning your back on the bear.
Obviously, teach all of your party these same things, as well as the importance of not hiding food in their personal packs or tents, using the bear bag, and disposing of garbage properly.
