Bigmon, I have experimented with all kinds of configurations in three different bore sizes and I have some 24 Ga.(.58) plastic shot cups if you want some. Lemme know.
This is what is called, "The Sky Chief Load"
Powder charge
Nitro (hard) card
Shotload
Thin overshot card
Full fiber cushion wad*
*The cushion wad needs to be SATURATED (the wetter and heavier, the better) with oil. I like to use olive oil.
I have experimented with this configuration as well in three different gauges, with great success.
I don't understand it, but it definitely works.
Robby