Why are we talking about squaring bore diameter to calculate bore volume? The formula for volume of a cylinder is pi (3.14159) times radius squared times height. Of course, our volume is constantly increasing as the wad/shot charge moves down the bore. Pressure is variable dependant upon the ever increasing bore volume AND the burning rate of the powder used. Boyles Law or Pascals Principle might be more applicable if we were dealing with say 9000 psi of compressed air or CO2 as our pressure source. We are assuming perfect obturation of the wad with zero blow-by as we transition from smaller to larger bore section. So without actual extensive and expensive testing, a lot of our assumptions are based upon conjecture and educated guessing. As such, I am not ready to admit that any of my assumptions are incorrect, nor would I wish to put my foot in my mouth and claim anyone else is wrong. It's all very interesting and I hope it inspires someone to do the actual testing to give us definitive answers.
