In my opinion, a smoothbore muzzleloading shotgun is far and away THE most versatile blackpowder firearm you could ever own. Just like its breechloading counterpart, the blackpowder shotgun can be used for everything from birds to rabbits to deer or bear.
As a matter of fact, one of my favourite pastimes as a kid was to go "tent caterpillar" hunting. These critters would make huge nests in trees, and when they hatch would devour most of the leaves. I used to load a light charge of blackpowder, a wad, a charge of fine sand and an overpowder wad and BOOOM! One mangled caterpillar nest and zero damage to the tree (other than cleaning the bark really well!)
I really like my side-by-side blackpowder shotgun for deer hunting, too; I have two shots instead of one, and load one barrel with a charge of 00 buck and the other with a rifled slug. If the deer is 25 yards or less, he gets the buckshot barrel and I can easily keep the slug into a deer sized target out to about 60 yards.
I use pulled Winchester foster-type slugs, coat them with moly-graphite lube and load them over a stiff charge of blackpowder and these shoot VERY accurately out of my shottie.
The only thing you MAY not be able to do with your shotgun is waterfowling, as steel shot is required and you have to be very careful if you plan on using steel out of your blackpowder shotgun. (Make sure you use shotcups designed for steel shot and don't let the shot come in contact with the bore.)
Anything you can hunt with a breechloading shotgun can be hunted just as effectively with a BP shottie, and the versatility you get with your in-the-field handloads is amazing. I highly recommend it!
