Guns Modify P Mags MWS

[Charlie36]

Has anyone got a fix for a GM P Mag MWS that only takes about 2 seconds of gas before stopping itself filing anymore? It shoots about 5-10 BBs before running out of gas, even though I have held the gas canister against the filler valve for 20 seconds 

 

[Hunka1988]

Have you tried venting as you fill? Briefly hold the knocker valve vent the gas and any air that has built up