Raimey,
Which rifle are you asking about? It the 8x48R S&S "1871 Bolt Platform" or the Remo KLB rechambered 8.15x46R? If it is the 8x48R S&S, use shortened 30-30 cases as described above. If it is the Remo, do what I did with a different KLB that was rechambered with a 30-30 reamer and had the neck opened with a straight reamer far enough to chamber an American brand of 32 WCF cartridge that had a heavy crimp and was damaged by shooting it with 32 WCF from a different maker, whose cartridges weren't crimped as heavily and the cases "jammed" into the front of the chamber, building up chamber pressure. I think I showed you the rifle. The way I figured it out was by forming a 30-30 case in a 32-40 die and loading a bulletless fireforming load. The fireformed case showed where to trim the cases to fire 8.15 mm Nominal bullets (sized to groove diameter). A chamber cast might show how much (if any) to shorten 30-30 cases (rims might or might not need thinning). the 8.15 groove diameters vary pretty widely so you should "slug" the barrel to find the bullet diameter you need.
Mike
