I agree with all answers you have received so far. i have used substitute powders in my flintlock, but I always dump 10 grains of FFFg black down FIRST as a priming charge, so they go off on schedule! I have found that FFg or FFFg can be used in the pan, but seems to fire slower than FFFFg. In the days of flintlock military muskets, the soldiers primed with a little of the powder from the main charge (carried in paper cartridges) BRFORE they poured the rest of it into the barrel and rammed the ball! Not too safe a procedure, but in battle, it makes for a faster reload time! They didn' t carry finer grain priming powder separately, just a paper cartridge with powder and a ball in it.