Black Powder Shell Reloading

[Cold Spring]

Originally Posted by Paul Harm

3 drams is 82 grs of powder, normally 2F for a shotgun. I also use 72grs of 3F seeing how it burns faster and will give about the same velocity [ and it's cheaper to do so ]. (snip) .

When black powder burns its weight (mass) is converted to combustion gases and relatively inert solids. The kinetics of the reaction dictate that 82 grains will produce more gases and solids than 72 grains. I understand the 3F burns faster than 2F and with the same charge weight will develop higher initial breech pressure, but why do you think muzzle velocity would be about the same with 72 grains of 3F as with 82 grains of 2F?