Rudy,
If you succeed to make paper shot cups, make some shallow ones, only 3-5 mm deep, and put them over the powder, under nitro card wad. Then you will have a gas seal wad that predates plastic version (on the bottom of one peice wads). This was worked out long, long ago (decades, century+?) to provide gas seal for bores not sealed properly by ordinary card and fiber wads. Sometime between WW1 and WW2, some USA ammo companies started to use these paper gas seal wads. I remember them from 1940s and 1950s, even later in Winchester-Western shotshells. There was once such gas seal wads from Sweden sold in USA, known by some as Swedish cup wads.
There are lots of ways to "beat the devil around the barn".
Niklas
