Perhaps a better way to say is that all paintballs require the same amount of Force to be propelled, as does the hammer need a minimum amount of force needed to reset itself. Since Force is equal to pressure times volume with gas, they are inversely proportional. Meaning if you raise one, the other must lower for the force to be the same. For example, if you lower your pressure, you need the valve to be open longer for more volume to give the same amount of force.

Since stock A5's don't have a built-in regulator, the pressure is constant at around 800psi. But since the friction is reduced, the hammer hits the valve faster, which creates a larger force (force for objects = mass x acceleration)(in this case, same mass times larger acceleration) on the valve pin. If the valve stays open for a certain amount of time before the polish job, it should stay open longer if it has a larger force hitting it after the polish job. That should yield a longer open time for the valve. The same thing happens with a stiffer spring; it keeps the valve open longer.

Since pressure is constant and the volume has been increased, the force has been increased on the ball, thus making it accelerate faster.

Rather than being able to control the pressure directly, I'm guessing that stock guns can only add turbulence and are wasting the excess air that isn't being used to propel the ball. Whereas those with a regulator are wasting none.

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