PAUL,
THERE HAVE BEEN A SERIES OF ARTICLES BY SHERMAN BELL IN THE DGJ THAT ADDRESS YOUR QUESTION. HE HAS A NUMBER OF LOADS FOR YOU TO COPY. FURTHER, REPUBLIC CARTRIDGE CO. SELLS 2 7/8 10 GAUGE BLACK POWDER LOADS IN 4 1/4 DRAM SWISS OR 4 1/2 DRAM SWISS THAT SHOULD WORK FINE IN YOUR GUN. I USE THEM REGULARLY IN MY OLD ELSIE AND IN A LEFEVER. CONTACT ME AT rolextjr@juno.com and i will send you some of his recommended loads for the 2 7/8 inch 10 gauge.
Tom Regal

Luck is the residue of good intention and hard work.