.45 ACP in moonclips in a spare cylinder for a Schofield.

[pony express]

If your determined to use black, standard procedure is just fill up the case far enough to get a little compression, about 1/16 inch is probably enough compression with that small of a case. That load won't hurt your smokeless powder Webley, but I can't say how many shots it will fire before binding, since I've never shot one, with any kind of powder!

[Virginia Gentleman]

What puzzles me is why your buddy won't buy some smokeless powder and handload it?  It is not an excercise in re-engineering.