Greetings!
I've had great success fire forming .348WCF to .45-75-350; before I moved and had to put stuff in storage, I was in the process of doing the same for my Chaparral 1876, .50-95-300. As I recall, I annealed the brass, dropped a charge of Unique, seated a wad of tissue on that, and a little Elmer's glue in the neck. It fire formed rather well, but was "wasp-waisted" near the web. My intention was to trim, seat a bullet over a "standard starting-level" charge of 5744 to finish the fire forming process.
I should dig those goodies out and finish...!
M.T.M.