I recall from an article in the American Rifleman from many years ago on Shotgun Propellants that the PB stood for Porous Base, & had to do with its method of formulation. As to its burn rate it falls in a medium category, more progessive than powders on the order of Red Dot, but less so than those as mentioned 7625, Herco, BlueDot etc which are the true progressive powders. It is a most excellant powder & should serve well indeed for the purpose mentioned & is much less temperature sensitive than 7625.
