Congratulations !
Shooting a flintlock pistol with Pyrodex and hitting a pie plate is quite an accomplishment.
I suspect that you aren't shooting real black powder because you haven't found any in your area?
If so, try again.
Dealers cannot have real black powder sitting on their shelves in the store so you have to ask for it. Many gun supply stores don't carry it at all because of all of the regulations that go along with selling it so use your telephone and call any and all of the dealers in your area.
While you have them on the phone if they say they don't carry it be sure to ask them if they know of anyone in the area who does.
With luck you might be able to find a pound of it.
Although your flintlock pistol will work best with 3Fg powder if the only black powder they have is 2Fg, buy it. It will work much better than Pyrodex or any other synthetic black powder.
Even if they only have some cannon powder it will be more reliable than any of the synthetic black powders.