Pleasure & good luck.
If you cannot get the cupped gas check wads, a 3/8" drill on standard fiber cushion wads will do pretty much the same thing in keeping the ball in the middle of the bore.
Make sure you have a hard card between the BP and the plastic wad.
Black powder flame will melt the plastic and spray your bore with it as a thin coating. Happened to me.
I was able to remove it with a "tornado"(spiraled) stainless brush, likely made easier due to the smoothbore. Rifling might really suck if coated with plastic.