Buffalo Bore 45-70 brass is made by Starline for Buffalo Bore and is a custom product. Tim Sundles developed the brass with a doubly-recessed small rifle primer pocket designed to accept the CCI No. 41 military spec small rifle primer. This primer is an anti-slamfire magnum primer. Sundles developed this configuration to virtually eliminate the possibility of a tube magazine detonation. Use any load data you choose, but because you have substituted a component, reduce the starting load by 5% and work up carefully towards the maximum charge watching for signs of excessive pressure or velocity. In any event, the magnum-like CCI No. 41 small rifle primer is likely to generate ignition in a similar fashion as a large rifle primer. And remember that Starline brass is about the thickest 45-70 brass available with a resultant reduction in case capacity compared with WW, RP and Federal. Glad I could help.