I've been using nothing but GOEX 3F. When I tested 3F a couple summers ago, I found 2F to give slightly higher speeds and less pressure, of course.
I guess I need to do some chronographing & accuracy testing with 1 1/2F Swiss and maybe some OE 2F if I can get it at the local show, next month.
I suspect that Forsythe's "Halls #2" is about the same as FFF. But I also expect it was better powder than Goex. I wonder if OE smells the same as other black powder does.
If I use powder that produces flakes of fouling in the bore the Nock breech in my 16 bore will not work. A flake of fouling will fall over the passage to the antechamber and priming had to be worked through the vent to fire the rifle. I have only tried Swiss and Schuetzen in the rifle and only Swiss is reliable never producing any problems. The Schuetzen would only shoot 2-4 shots before the breech was blocked and the rifle would miss fire.
This link might be of interest when comparing Europeans and American granulations.
http://www.blackpowder.ch/powder/shooting-powderIn the old days, I have read, the "F"s indicated the granule size and the "G" indicated "graphite" or "black lead" as it was called. The British military for example would not accept powder coated with "black lead".
Note the recommendation of the use of very fine grained powder in pistols. Back in the day this was common in both percussion revolvers and I believe in brass suppository cartridges for small caliber handguns loaded with BP. The granulation for percussion revolvers was "Revolver" and was about like FFFF. But when used with cartridges for percussion revolvers these had light charges since the paper or other cartridge material reduced the powder capacity. They also used elongated bullets much like the pointed "Picket" bullet used with a cloth patch in ML rifles. This also reduced the powder capacity since they were long for their weight.
I have also read accounts of shooters using very fine grained powder in rifles later in the ML era. IIRC "5F" was mentioned. But would have to dig to find the citation. Dillon, Cline or Roberts? Just don't recall. But I suspect these were 28-36 caliber "squirrel rifles".
Dan