Harry,
I believe that the problem may, in part, be with your "understanding" of the "open plains" and perhaps in the distinction between "just about the only fuel" and "the only fuel" available.
I would also refer you to the "Encyclopedia of Buffalo Hunters and Skinners" by Gilbert, Remiger, and Cunningham. There are numerous references to reloading of ammunition, reloading "outfits," and molds. Also numerous lists of provisions procurred by the hunters, most of which included "lead" usually in 100 pound weights.
Also, just for fun, I would refer you to "The Champion Buffalo Hunter" by Victor (Old Vic) Grant Smith.
There are others, but if you are interested, these will get you started.