We xdm half firing

[joshcowin]

Hi their i have a we xdm and it has been great until now. It is firing a few shots okay but then all of a sudden it fires but the slide does not do a full battery it just moves back 2 inch and you hear a hissing of the gas mag. I release the mag and re cock it and its fine again. Im using nuprol red gas could it be that the valve knocker spring isnt strong enough to fully hit the striker? Thanks josh