JC,
If all the other variables are held constant, that would be the only way I'm aware of to change pressure to such extremes. This is reflected in loading manuals where pressures show extremes while payload and velocity are constant.

Jim,
I think the physics behind what I've stated are pretty solid; "for every action there's an equal and opposite reaction". The differnce in acceleration of the gun has to correlate with a differnce in acceleration of the payload. If exit velocity of the payload remains the same, total energy of the firearm recoil remains the same, I've always agreed on that point. The difference of opinion here is really just about whether a 'mere human' can percieve any difference of loads where pressures go from one extreme to the other while maintaining other factors.