I think the comments of Iron Jim, above, are the most interesting comment posted to date. I have used a 1/8" overpowder card in my 20 ga. fowler, and it does a very good job of sealing the gases for both shot and RB loads. But the idea of using only overshot cards, or wafers, to eliminate carrying extras in the field is intriguing, and his method of loading makes sense. I am going to have to do my own testing, of course.
I have used felt wads in my 50 ca. rifle, However, they don't alwas seat properly and I still get an occasional flyer, and burned patchs. Up until now, I have only loaded ONE felt wad, so Now I need to go back and try loading more than one, to see of that helps seal the bore completely shot for shot.
If the felt wad works, the weather stripping you can buy in rolls would be a cheap way of acquiring the felt needed. All you need is a bore sized punch to make your own wads.
I prefer using beeswax and olive oil for a lube to soak the felt wads in. Beeswax is softer and less brittle than parafin. YOu can use something like crisco also, with the beeswax, to cut the cost down even more. ( use the lard-like crisco, and not the liquid. Just heat the beeswax and oil or lard in a small can that is put into a frying pan full of water, to created a double boiler effect. Otherwise, you might heat the wax too much and start a fire. When the stuff is all melted and you have skimmed the top with a spoon, just put the felt wads in and push them down so they soak through completely, then take them out, strain them, and put them on wax paper to cool and dry. YOu can do hundreds of wads in just one setting, making this a once a year chore, even if you target shoot every month. I use a washed and dried out cat food can, because I have so many of them every day, and when I am tired of melting wax and oil, I just turn off the neat, remove the small can from the boiling water, and let it cool. If you have large quantities of the mixture on your wax paper after removing the cooled and dried lubricated wads, you can scrape the excess off into the pan before you cool it down, and save it in the can as I do. Or just through the wax paper and extras away.