Cold Springs, think about what you wrote. If 3F produces more pressure that 2F, then wouldn't a little less 3F produce about the same as a charge of 2F ? I've never checked velocity of my shotgun shells, just going with what others have used in the past. Go over to
www.doublegunshop.com and do a search or ask the question about BP loads for shotguns.
You can do the same thing with rifles - a little less 3F and get the same results as with more 2F. The 2F burns faster - don't know about all that " When black powder burns its weight (mass) is converted to combustion gases and relatively inert solids. The kinetics of the reaction" - I just know what works. At least I think I do - most the time.