Mr. rock scratcher,
Yes, it is a 20ga. We use a PRB dropped from a .600 mold, cast from wheel weights. Off hand, I don't know how thick the patch is but it is a snug fit. 90gr of 3F GOEX down the barrel and in the pan gets the job done out to 50 yards, perhaps a bit further. This load is safe in our gun and pleasant to shoot. I don't know if it would be in yours. With all due respect, you need to check before using!
For shot we prefer #6 (don't remember exactly how much our measure throws) with a thick over powder card and one thin over shot card, powered by 70 gr of 3F. There are a lot of possible combinations that will work quite well.
Best Wishes