[FrankenMauser]

I don't use shot cups or plastic wads or gas seals in BP loads. I don't want plastic anywhere near my BP bores.

I generally load BP shot shells with classic "square" loads - powder charge and shot charge are of the same volume. I use 1F or 2F Goex, Swiss, or home made BP.
Wad column (nitro card, fiber wads, and maybe cork on top) is adjusted to get the overshot card where I want it (or to get the fold crimp correct if I am doing one-time-use loads in plastic hulls).

Right now, I only have 16 ga loaded. So I don't have any specific data to share for 12 ga.
I do believe a common cowboy action load is 7/8 oz shot over 65 gr 2F. Wad column adjusted for the hulls being used.