Greetings!
I believe that I was watching something on cable... I want to say that it was "Tales of the Gun", but I could be wrong. A CW Reenactor was pouring powder into a primed case, and seating a lead ball with a pair of large channel locks!
Perhaps a lead RB could work O.K.; personally, I would drop-tube the powder, seat a thin card wad, add a lube cookie {or smear RB with lube}, and press in a RB of around .515".
With the light charges of a Spencer, you might get some accuracy; but you will need to contend with the fairly fast rifling twist coupled with the minimum bearing surface of a RB. Single loading will also probably be necessary.
If reasonably successful, this would be a fun, bare-boned, cartridge that could be assembled in the boonies with minimal tools: Loading Block, Decapping Rod, Mallet, Dowel to seat a new primer, Powder Scoop {or BP compatible Powder Measure} & Drop tube. Assemble the round, and press the RB down on the Loading Block to "seat" it; this woulb be the biggest variable, as you'd have little control over seating depth/powder compression. This could be overcome by drilling a hole in your loading block tight enough for your cartridge rim to "headspace" on, and drilled to a satisfactory depth to uniformly seat the RB. The pressures involved would more than likely eliminate the need for sizing the brass.
This is the kind of "reloading" I did as a kid, and for up-close stuff, it works suprisingly well. Hell, I may try this with my Spencer!
Be Well!
MTMarfield
11-27-05