ldholton,
I'm not sure I understand your last two questions, but pressure and velocity are related in shooting a shotgun shell, similar to with a rifle cartridge, but a little different.
The wad is like a piston traveling down a tube, pushed by expanding gases from the powder burning.
The velocity of the shot (and wad) is related to the acceleration. For a wad initially at rest,
Velocity (ft/sec) = Acceleration (ft/sec/sec) x time (sec)
That same acceleration is associated with the pressure:
Force = pressure (lb/ square inch) x area (square inches)
and
Force = mass (lbm) x acceleration (ft/sec/sec)
So,
Pressure = mass x acceleration / area
The above involves some simplification because none of the terms are constant (they vary with time) except the mass of the shot and wad and possibly the area of the base of the wad.
The tightness of the wad determines the amount of gas that blows by the wad instead of pushing on the base of the wad, which affects force on the base on the wad, which affects pressure and acceleration, and ultimately velocity.
Pressure also has a role in slightly deforming the wad to seal against the walls of the tube (barrel), which in turn means more of the gases are pushing on the base of the wad instead of blowing past it.
Edit to add:
Before anyone points it out, yes I did neglect some of the forces like friction and glossed over the Newton's 3rd law discussion for why the wad/shot mass acceleration is approximately equal to the force from the pressure of the gases on the rear of the wad, for the sake of simplifying for illustration purposes.
Understand completely what you're saying let me try asking this a different way.
Take longshot versus Red Dot
Long shot will produce very high velocities at fairly low pressures. Will Red Dot will produce lower and moderate velocities at much higher pressures. Which one of them was most likely to cycle a gas gun the best? Or will it really make any difference is the cycling base just on mass of projectile and speed? And the pressure has little to do with it or does the pressure affect some?
