Let's help the guy out:
Fg, also written fg, means fine grade and is used in cannons and some fireworks. It is not for use in rifles or handguns.
FFg, or ffg, is fine, fine grade and is intended for use in large bore rifles (.50 cal & up) and shotguns. It can be used in pistols and lower caliber long guns with some reduction in performance.
FFFg, or fffg, means, well, you get the picture. It's intended for use in pistols and small bore long guns. It can be used in large bore long guns with some reduction in performance, depending on the target, range, etc.
FFFFg, or ffffg, is the finest granulation and used almost exclusively as priming powder in flintlocks.
I suggest you get some FFFg real black powder or Pyrodex P for use in a pistol.
And please do read the Black Powder Essentials sticky. It's most informative about many, many things.