Converting a Gas Blow Back Rifle to use HPA Tank

A few months ago I was approached by a friend and fellow airsofter Alan. He wanted to see if I could convert his WE PDW Gas Blow Back Rifle (GBBR) to be powered by an HPA tank. He also wanted the gun to have a hi-cap magazine to extend it’s number of shots between reloading. I actually had very little experience using GBBRs but I thought it would be a pretty interesting project. After examining the gun and the firing mechanism it was apparent that the HPA tank would need to be attached to the stock gas mag, and a hi-cap magazine would need to be mated to it somehow. I realize this isn’t a new or unique idea and after completing the conversion I discovered on you can see several similar modifications on YouTube. Nonetheless, I wanted to share my implementation of a GBBR to HPA tank conversion.

I added the HPA connector by drilling and tapping 1/8 NPT hole in the bottom of the gas magazine. To have the high-cap magazine feed to the gas mag, I used an extension spring with .312″ outside diameter and .026″ wire. I cut/milled out the gas magazine BB channel to accept the feed spring. I added small cut rubber pieces to keep the spring centered and held in place. The high-cap mag is attached to the gas mag using a screw down hose clamp. Other methods that are “prettier” could be used, but the hose clamp holds the mags very securely and is easy to remove if maintenance or adjustments are needed. The feed hole on the hi-cap was drilled out to allow the feeding spring to be used. To make winding the hi-cap mag easier, Lonex Flash mags were used so just a few pulls on the winding cord and the magazine is fully wound.

The gas blow back rifle with HPA tank is very air efficient. At approximately 80 psi, the gun shoots in the low 400s FPS w/.2g BBs.

Here are some pictures of the conversions I did for Alan (WE PDW) and also for Marcus (WE L85):

Sid M. WE PDW HPA Conversion

Sid M. WE PDW HPA Conversion

Sid M. WE PDW HPA Conversion

Sid M. WE PDW HPA Conversion

Marcus F. WE L85 HPA Conversion

Marcus F. WE L85 HPA Conversion

Marcus F. WE L85 HPA Conversion

Marcus F. WE L85 HPA Conversion

Marcus F. WE L85 HPA Conversion