I know thats smokeless pwd is rated on its burn rate. How is black pwd and pryodex rated. For instance is say pyrodex p slower burning than say rs, or t7 and so on?

The powders for muzzle loaders are rated in grain size. The smaller the grain, normally the faster the burn. Of course the chemical make up of the powder would also effect the burn rate. But for example;

Black Powder
F1 = cannon powder & very large bore muskets
F2 = rifle powder for .50 caliber and larger
F3 = rifle powder for .50 caliber and smaller. Also used as pistol powder.
F4 = is normally used as a pan powder because of the flash ability
F5 = and above in grades are often used in the blasting powders and will flash burn.

Pyrdoex RS = stands for Rifle & Shotgun is is considered a 2f grade powder
Pyrodex P - pistol powder it is considered a 3f grade
Pyrodex Select = is RS but sent through a sizer a couple times more so the powder is more uniform.

In Triple Seven and the other powders they are normally grades.. 2F or 3F. Again, it relates to their flash time, and their pressure peaks.

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

Thanks fellers I wasnt sure which was the faster burning. Black pwd and pyrodex P is all that I have ever used. Picked up some RS and T7 2F to give a try and see how it shoots in my rifles.