I use reformed 348 brass to make 45-75 cases. It is relatively inexpensive, lasts forever, and works in all of my rifles.
To reform the brass, I use a set of expansion plugs that I obtained from C&H Die and Tool.
Once the neck is expanded to 45 caliber, I trim to length, full length size and load. First firing or so, fire forms and sets the brass. (Note: First trim should be
at least 1.90, as the case will "shrink" with the first firing. Once it settles in, 1.88-1.89 will work in anyones rifle.)
From left to right is a formed case, a reload and an original 45-75 cartridge for comparison:
I hope Hobie will return with his method which uses 50 Alaskan brass, and is a bit less time consuming than my method.
In addition, factory reloads are available from Ten - X in either BP or smokeless loadings. Hang on to your socks when you hear the price!