The problem I seem to be having is that when the piston has sealed against the barrel and the gun has been pumped up, all the air within the gun is going out the sprinkler valve outlet.
i.e- No air is going out the barrel.
I thought it may be because no air was getting past the piston and into the chamber, however, on other shots the piston will seal but only till about 30 psi at which the piston slides back and lets the air out the barrel without me venting the pilot, i.e I am not venting and the piston still opens.
The barrel is 1m long the pipe is 15mm, the chamber is 50cm and the pipe is 25mm, and it is vented by a modified sprinkler valve. I'm not sure of the pilot volume, it is approx. 10 cm long and 25mm pipe Any input as to why my gun is not working would be helpful.
Thankyou.
Here are some pictures...I hope.


