Yes, smoothbores will shoot better than most people would suppose. It just requires the shooter to take the same care in loading that you would with a rifle. It will also require a little experimentation to figure out an optimum load.
As for black powder substitutes, I guess if you have to use one....you have to use one. I personally dislike Pyrodex, just as dirty as BP and MORE corrosive. I have heard some good things about CleanShot, although I have not tried it.