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.