Arsanus does a tutorial video to help you install the RA-Tech NPAs into WE Airsoft M9 Gas Blowback Pistol... "An In-Depth Tutorial on how to install a RA-Tech NPAS into your Gas-Blowback Pistol. This method should work on most Tokyo Marui/WE Gas Blowback Pistols and WE Open Bolt Rifles.
The Airsoft Pistol shown in the video is a 'WE-Tech Full Metal M9 Heavy Weight Airsoft GBB Pistol'.