gregrn43
There is no "per say" rating, and since different based propelant reacts differently to different situations it is sort of by feel after you get past a certain point.
Black FFF and the P grade of pyrodex along with the FFF grade in other subs were originally designed for pistols short barrels and small calibers black actually has 4 grades FFFF priming powder for flint locks FFF pistol and small calibers [up to 45] FF for larger caliber rifles and shot guns and
F cannon powder.
The exception to this type is the new Blackhorn 209 which is a progressive burning cellelose base powder [ as compared to consistant burn of black and other subs] while I have never attempted to use blackhorn in a pistol as I have no pistols that us the proper ignition I know it works well in short barreld rifles It actually shows about 7 percent less pressure than 777-FF while producing a bit higher velocity than FF its about the same as 777-FFF in velocity [ this is assuming proper fit and ignition].
I hope this helps. Lee