Originally Posted By: 2-piper
IMR stands for Improved Military Rifle powder. 4756 & 7625 were classified by Duont as Sporting Rifle powders, thus SR. I believe that PB was classified as a Shotgun Powder. In any case the PB designation related to its mode of manufacture & stood for Porous Base.


Miller I think you are correct on the origins of PB, however, today it is marketed as IMR PB.

Last edited by TwiceBarrel; 01/18/11 02:01 PM.