I seem to recall that the "f" designation is a modern invention. All the old accounts I can recall refer to "strong" powder and some such, but zero mention of grain size. Haven't seen Spence post in a while, but he's a gold mine for original references.
The most striking thing I recall about powder from that era was a report from Lewis and Clark about powder wetted in a boating incident. They spread it out to dry so they could go back to using it. Never tried it, but that makes me believe the grain size was pretty large. When I've managed to wet powder here in our rainy climate, it's turned to soup and would make better paint than shooting stock.
