SpudFiles

with all the air passing through the barrel port and the piston dumped in the back, I never thought it would re-close...

If the pilot vents at a moderate rate and the chamber vents at a high rate out a larger orifice, it is possible to have the pilot at a high enough pressure to force the valve back closed. A valve honking or going put put put is the symptom. This is common in valves with a large OD in relation to the valve seat diameter, such as sprinkler valves.

Air cannon honking.. This is a valve that closed many times when fired. Skip forward to 45 seconds.
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Though you must remember that "honking" is not necessarily bad. Many valves will honk once the ammo has cleared the barrel. That has no affect on the gun's performance.

Of course, if you would prefer your gun didn't sound like someone stomping on a goose ...

Is this jsefcik in disguise and or incognito trying to act smart and use bigger words?? :glasses5: