Your flintlock would prefer the FFF anyways.. especially in foul weather where coarser grains leaves room for humidity to enter.

80 grains of 777 FFF keeps my roundball butter-lubed pillow-ticking patches almost reusable. I shoot 100 grains 777FFF Powerbelts with no signs of butchering the plastic base. You won't be wasting your money if swab with fast-drying watery agents & keep the bore walls dry from contaminating oils & lubes. Just curious! What 3F or 4F powder are you putting in the pan?