It is possible to grind it finer but that is not desirable for use in artillery. Even FFFFg is too fine for anything other than bb size (steel air gun shot like for a Daisy, not bowling balls.) Use the same size granulation as you would for a muzzleloading gun of a given caliber. Once you get over 1.25" bore, use Cannon grade, although you can use Fg for golf balls in that caliber or even FFg for golf balls in golf ball mortars.