I think there another point to consider. If you use 3F or 2F in the pan of an early flintlock rifle, or fowler, with a good size lock, and large flint, in it, I seriously doubt you could feel the difference in how quickly the gun actually fires. On the other hand if you are trying this with a late flint rifle, or pistol, with a small lock, and tiny flints, you may experience slow fire, or no fire. I only use 4F in some of my tiny traveler type pocket pistols, because they just aren't reliable with courser granulations.
Hungry Horse