It's good to stay with what is readily available. Note that different wad systems allow for differing crimps.

I was able, in my loading for 12 bore double, long ago, to use card and the base cup wads cut from AA12White trap wads. The base cups made a perfect cradle to hold my round balls centered in the bore. I adjusted the card and fiber wads to fit. If at all interested in round ball loads, I placed a cut-ff base cup, cup down against the powder, then fiber wad, then another cup, cup-up to hold the ball. I then fold crimped my cases. I adjusted the powder charge for a 1,500fps load with the almost 500gr. ball.

I was able to shoot groups well under 10" at 100 meters with this load - and 12" offhand. I did mount a 2 1/2X to 8x scope for load development. This made hitting at 100yards quite easy.

One of the locals needed the gun more than I did, so he gets his moose every year with it.