[RRLedford]

Not sure what "blocking the cylinder" actually is, but to have most of the air ahead of the retracted piston be gone when you want to fire the piston with max. peak velocity, you either need to evacuate it with a vacuum pump, or seal the exhaust port when the piston is full extended and then pull the piston back into the cylinder, creating a vacuum inside the cylinder as it retracts.

This demands some kind of retraction mechanism combined with a trigger hold/release mechanism strong enough to retain the piston with 120 psi behind it. Venting pressure during retraction and reapplying it after retraction allows for the retraction mechanism to be weaker. The key factor is to have a cycle that maintains as little air in the cylinder as possible when piston is retracted and ready to fire.

Having to push out almost no air from the cylinder, ahead of the piston disk as it accelerates gives a serious boost to peak velocity, and lengthens time in contact with the ball.

-Dick Ledford