The Staghorn is a hammer striker model and not recommended to shoot BlackHorn 209. The problem is the primers can blow back into the face of the shooter. I can personally attest to this with a Black Diamond and dug the center of the primer out of my forehead. Not a pleasant thing to do.
Instead, just load 90 grains of Pyrodex RS and a good sabot combination, swab between shots, and clean it the same day you shoot it. Don't worry about having the new whiz bang powder. If you'd wanted that you should have invested in newer technology.