These are quick and simple calculations. I didn't include weight as I don't think it factors into this part of the problem. I wasn't trying for total friction force, only the numbers if the wad generated sufficient friction to block movement; one very special case. Forcing cone friction should closely follow the barrel bore. Chuck gave us some real numbers for plastics closely related to wad materials. Also, the wad will quickly heat from the friction and powder gas. My guess is that friction will go way down due to surface lubricity as the wad heats.