I'm trying to repair a Maruzen P99 (the gbb) for a friend and I'm entering into new territory trying to work on GBB's. Right now the gun has the following issues: 1: It seems like it is double feeding, or would be double feeding if it was working. If I put a loaded magazine in and try to rack the slide, the slide will stop just short because more than one BB is leaving the mag, one goes in the hop-up while the other goes freely into the ejection port area and prevents the slide from coming forward. 2. I'm not sure whether I'm not getting a good fill on the mag or what, but when I try to fill the mag with propane and use the gun, I get a wimpy half-powered cycle that doesn't even make the bb leave the hop-up. I need help on this from more experience GBB techs than myself. The one thing I do know is that the fill valve on the mag seems to be opening alright and the O-ring in the mag looks OK as well.