Hah I've checked but 5lb minimum. 1lb is more than enough for what I need after that it'll just be too expensive. I've already got 50 rounds of 577/450 loaded with Pyrodex, was just looking for something more historically accurate.
1.) Once you start shooting, one pound ain't gonna last long.
2.) You should be beaten about the head and neck with a pipe for defiling the magnificent Martini-Henry with horrid BP substitutes.
One must use the Holy Black.
You are a heathen for doing such sacrilege.
3.) You can economize BP use by mixing cream of wheat with the BP when you load your cases.
You just gotta make sure the case is full of powder and slightly compressed.
Easier on the shoulder as well.