Webster's Online Dictionary
"In the USA, standard grades of black powder run from the coarse Fg grade used in large bore rifles and small cannon though FFg (medium and smallbore rifles), FFFg (pistols), and FFFFg (smallbore, short pistols and priming flintlocks). "
The above information is not correct. Accepted grades for calibres are: Up to .45 calibre 3FG. .50 calibre & larger 2FG. Same for pistols. 3FG can be used in larger calibres providing the recommended powder load is adjusted to lower the pressure. 4FG should NEVER be used as a main load, NOT in any ammount. This 4FG is a very fine powder & a modern invention to be used to prime the PAN on flintlock guns (priming horns & special priming powder was not used in the 18th century). If you were to load a gun with 4FG/ffffG, it will likely explode the barrel causing death or injury to anyone standing in the close vicinity.
PLEASE NOTE: There is no contact address on the above site, so I am unable to contact them & correct this error.