Try two different ways: The single biggest problem shooting out of any gun, choked or not, is getting rid of donut hole patterns. Without the plastic shot cups used today, you just can't send the shot out as fast as modern loads do. In fact, you need to stay below the sound barrier(1100 fps) to get the best patterns.
Try using one OP wad( 1/8" thick) to seal the gases, then a 1/3 to 1/2 cushion wad( take the normal cushion wad, made of celotex, and split it in 2 or 3 parts. Then lubricate it with olive oil or your favorite lube). Then put in the shot load, and then a Overshot card. As for powder and shot loads, begin with 1:1 loads, using the same volume measure of 2Fg and shot. The choice of shot is determined by what you are hunting just as it is with a modern shotgun. If you have holes in your pattern, try changing the ratio of powder to shot, say 9:10( ten percent more shot by volume than powder by volume) or 4:5. In a 12 gauge, start with 2 3/4 drams of FFg powder( 75 grains approx.) That setting will give you a little more than 1 oz. of shot. In a 20 gauge, try 60 grains of powder, and 7/8 oz. of shot. Read Bob Spenser's website, Black Powder notebook
[url]
http://members.aye.net/~bspen/index.html[/url]
particular BOTH bob's article on loads, and that of the late V.M. Starr on shotgun loads. You will be surprise, I suspect at how light the powder charges are compared to modern loading preferences.
You might try using a heavily lubed cleaning patch to lube your barrel when you seat that Overshot card on top of the shot. This will lubricate the bore, protecting it front rusting, but also allow the shot so slide over, rather than rub off against the barrel. leaving both flats on the pellets, and lead in the bore. The lead buildup is responsible for making patterns worse as you continue to shoot, unless you take the time to work the bore with a bore brush between shots. Most of us don't do that until we are done shooting for the day, or the hunt is over. Carrying a small bag of prelubed cleaning patches is relatively simple, and experience shows that it does help to make the patterns round, and less ragged at the edges. That fills the inside of the patterns, so that you don't have gaps and holes.
The other method of loading is the one Jim Rackham has written about here, and that is to use only OS cards, using 4 of them on top of the powder to seal the gases; each OS card has an off-center hole punched through it with an awl. You can put a dab of lube under the 4 card, before seating it, and that will lube the barrel AFTER the shot has passed down the barrel. Next the shot load is poured in and then Jim recommends using 2 OS cards to hold the shot in place. Again the holes in the 2 cards are not aligned with each other, so that no shot leaks out, and air will help separate the adjoining cards as soon as they leave the barrel.
Even with this system, I recommend lubing your barrel as described above. I think it helps patterns to have them move across a greased bore, rather than rubbing lead off on the bare steel.
Experimenting with different methods is what this sport is all about. I use wonderlube to grease the bore. Olive oil has a higher flash point( temperature at which it ignites). Depending on where you buy your olive oil, and in what quantity, you can buy some of it fairly cheap. Stay away from the gourmet stores. If there is a " store brand " it is almost always the cheapest. Olive oil is olive oil for these purposes. If you cooking or mixing an oil salad dressing, then you want EVO, which is a lot more expensive.
