If you decide to use black powder, just find a volume that needs about 2mm or 1/16" (very rough estimates, basically a "tad") of compression to seat the bullet of choice and its cardboard wad (waxed is good here, generally). Originally, the bullets were paper patched, you may want to try that as well if you feel adventurous.

Patrick Chadwick may have some posts, search under his name. I'm pretty sure there was a lengthy thread about this cartridge that has been inactive for only a few months. I'd find it for you, but time is VERY limited on my end right now.