What my old Proline manual says on Adjusting Velocity

Here's what my old Proline manual says:
"To increase the velocity of your gun, remove the front mount screw, disconnect the bolt rod from the bolt found at the rear of the body, now you can slide the pump, pump assembly together with the bolt rod off the barrel. Remove main spring from inside the lower chamber. Replace the main spring with one that is slightly beavier in its compression. Now check your gun over a chronograph to measure the velocity."

"To reduce velocity repeat the above, but replace with a weaker compression spring."

Adjusting velocity by changing valve springs and the dwell time:
"The valve spring is located behind valve guide. Remove the rear mount screw. Pull out from the lower chamber the ASA donkey, inside you will find an exhaust valve and spring. Ensure the sealing surface of the exhaust valve is clean and free from any grit or swarf. By replacing the valve spring this will alter the dwell time. Dwell time is the period of time the exhaust valve is open. The shorter the time (heavy spring) the more efficient your gun will be. Over springing the valve will result in a decrease in velocity. A balance is required between the front main and rear valve spring."

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This excerpt is assumed to be ©copyright Arrow Precision.
Kwoklea Wu, Last updated June 15, 2000
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