I suggest you get a standard 12 gauge overpowder wad, and merely turn it on its side to push it beyond the choke. Then run it down the barrel to seal the powder. You will get a much better seal than using wonder wads alone. Use a lubed cushion wad- wonder wads are okay here, but they are expensive. I take a standard 13 ga. cushion wad, split in half so its only about 1/4 inch thick, rathern than the 1/2 inch thick it comes as, lube it with mineral oil, and run that down on top of the overpowder wad.Using the smaller diameter makes it easier to run it down the barrel, and it will be compressed enough on firing to lube the barrel adequately. Then I like to use an overshot card on top of that cushion " wadette", to provide a hard, smooth, and dry surface to push the shot out the barrel. But, others get good enough patterns simply pouring the shot down on top of the cushion wad. Pour in the shot charge, and then use a 12 overshot card to hold the shot in place. At the ranges you are going to shoot your improved cylinder loads, ( under 30 yds) you don't need magnum charges. Stay with 2 1/2 dram or 2 3/4 dram loads with 1 oz of shot. You can use as little as 3/4 oz, or as much as 1 1/4 oz. but a 1 oz load at that range is more than adequate in both pattern and power. You don't need the recoil of heavier charges, and the powder you use to get that recoil will just blow open the patterns, and provide little extra down range energy on the target. The difference between a 4 dram load and a 2 dram load is lost in the first 20 yds. Check the charts in the Lyman shotshell reloading manual, or even the data at the back of Dixie Gunwork's Catalogue.
