All you're changing is the length of the cushion part. The part where the powder sits, it's length or diameter, hasn't changed one bit so why would pressure change ? If you're going to insist it does, is it enough to make a difference ?
You do understand how a shotshell works, right?
After ignition, when the propellant thermally decomposes into gas, it encounters a moveable obstruction. The wad acts as a piston, which drives the shot load up the barrel. The 'cushion' section is just that, a collapsible section of the wad that increases the initial area available for gas expansion.
The peak pressure is reached before the shot even moves from it's initial position.
Contrast 2 extreme variations, one the red AA wad, the other the gray AA style wad designed for 7/8 ounce loads. Put the short wad in a short shell, put the longer wad in a standard shell. The area available for initial gas expansion with the longer wad and case looks to be about THREE TIMES as much with the standard case and long wad.
How in the world can pressures be even close to identical?
