ACM M500 Gas Shotgun HPA Conversion

I personally don’t have or use any gas powered guns (I’m having too much fun with Fusion Engine powered equipment), but when Todd Malan asked if it was possible to convert an M500 gas powered shotgun to use an HPA tank, I was intrigued. So Todd sent out his M500 shotgun to see what could be done.

The M500 is a pump action shotgun that shoots 5 BBs at a time. There is a small gas block in the main body of the gun that is charged up using green gas or propane, and it apparently lasts for a dozen shots or so. By converting this gun to use an HPA tank, it eliminates the need to recharge the gas reservoir, there isn’t any decrease in performance as you fire more shots, and it’s not affected by the temperature as much. Also, you can adjust the FPS by adjusting the pressure delivered by the HPA tank.

The trick to converting this gun to use an HPA tank is to find a location where an air line can be connected. Fortunately on the M500, the gas block has a large removable plug on the back. I attached a small fitting to this plug and ran a small air line around the trigger mechanism and down through the pistol grip. A few areas of the trigger block had to be milled out to make room for the air line, but there is enough clearance for the small tubing. The small diameter tubing (which has a 190 psi working pressure) can be used since it is only charging up the gas block. When the trigger is pulled, part of the pressurized air in the gas block is released to fire the BBs, then the pressure of the block is restored through the small tubing. High volume air flow from the HPA tank is not needed in this case.

It’s a fun gun to shoot, and with the HPA tank you can pump and fire until all the BBs are gone without a worry. I’m sure Todd will make good use of it in the CQB environments or in close range engagements on the field.

Happy Airsofting,

– captainbingo

Here’s the parts list: