RE: 4F Blackpowder--WTH is it?
The Continental Army's manual of arms (and probably that of most European nations as well) called for priming the pan and closing the frizzen witht he musket on half-cock, with a small portion of the powder from the paper cartridge BEFORE grounding the butt and pouring the rest of the charge down the barrel, to be followed by the ball. This sequence was good for speed, but not for SAFETY!! (This practice sometimes resulted in the priming firing before the barrel was loaded - thus the expression "going off half-cocked".)
They were therefore using Musket or Fg powder for everything, including priming. I suspect that if you use FFFg for priming, it will give a lock time so fast that most people could not tell you if it was FFFg or FFFFg that was used in the pan! The ONLY immutable requirement for priming powder is that it has to be real BLACK POWDER, not a substitute!