My shotgun is not a TC, but is a cylinder bore 12 ga. I ordered wads from Track 'o' the Wolf, and use Circle Fly 12ga. nitro card wad over the powder, split one of their cushion wads in half, then shot and one of their 11ga. overshot wads. (11 ga. is tighter and doesn't back off from recoil of the first barrel. You don't have that problem). I find a 16ga. load works well, 70gr. FFg and equal amount of shot. Mine patterns well to about 30 yards, then starts to open up and have holes in the pattern. Before I cut the cushion wads in half I got doughnut patterns. If you melt bullet lube (I use Pearl Lube i.e. equal parts crisco, toilet bowl rings and soy wax) and soak your cushion wads in it they keep the fouling soft and you can shoot all day without wiping.
If you want a good read go over to Cast Boolits and read the article by V.M. Starr in the muzzleloading room. Or google him up and his article is in other places as well. That man knew a thing or two about muzzle loading shotguns. One of these days I want to make a wad cutter and try his suggestion of the cardboard wads. If you only had to carry one kind of wad it makes hunting with your shotgun a lot more practical.