[akamikeee]

That is one made using the internals from an escort mp5, says so in the description, plus you can see the airshaft when he opens the cover and fires. That means the gun also runs off an external rig for the power source, plus you can see the hose running from the gun in the video. The video is over 2 years old so there should be some alternatives to making one, possibly modifying a DG M249 drop in kit.