What an absolue beauty.

Whatever you end up loading it with, have fun!!

There's always possibility for nitro for black loadings.
Have you cast the chamber yet?
Have you slugged the bore at the breech and muzzle?
Do you have ammunition, brass, or load data from it's previous owner?

A positive identification of the chamber and bore specs are important starting steps in working up nitro for black loads.

Again, what a beauty!

--Tinker