Originally Posted By: 2-piper
Upon ignition the pressure rises very quickly & then as the charge begins to move giving it more area it begins to fall off.


2-p, I know you know that "area" should be "volume." I mention it only because there may be some that don't understand that a change in volume will cause a change fluid pressure. Statically, increasing volume equal decreasing pressure. In the case of fluid flow, decreasing area will cause an increase in flow velocity and a decrease in pressure.

AS the shot/wad moves down barrel the volume containing the powder gas is rapidly increasing and the gas pressure rapidly decreasing. As the shot/wad transit the forcing cone, the pressure drops and the velocity increases. Ditto for the choke constriction.

DDA