My latest issue of "BPC News" has an article on this subject written by Mike Nesbitt. He says the troopers used 5 grains of black powder in their collar button gallery loads. He loaded some up with 7.5 grains of OE fffg powder and got about 430 fps velocity in his C. Sharps 1874 rifle. He then loaded some up with 10 grains of the same powder and got 559 fps. This powder was loaded loose in the case! I found a load of 5 grains of Unique in an old Ideal Handloading manual; that load gets out there at 900 fps!