DIY - Reduce FPS for GHK AKM GBB rifle

[N_Force]

Since the Ghk akm has high fps out of the box about 400fps+ , even changed to 1J nozzle, it's still around 380fps. To make it gamable less than 350fps for most of the airsoft field, I need to reduce the power. But this nozzle is sealed completely and no chance to add Npas for it. So I have to use my own way.

Based on the design of how the floating valve controls the gas flow and effect the fps. I figured out there are two factors, first is the tension and length of the floating valve spring, and second is the traveling distance and weight of the floating valve.


Spring of the valve: Stronger or longer spring allows longer time for gas flow through, means higher fps. Weaker or shorter spring will be lower fps.
Traveling distance for the valve: Longer traveling distance or heavier weight allows more air flow through, means higher fps. Shorter traveling distance or lighter weight will be lower fps.
The weight of the valve: most of them are plastic in light weight, also the aluminum too, may not effect much. Unless you modify and increase a bit, that could be.



Here is the concept for modify I figured it out.


The procedure will be in second post.

[N_Force]

First, Get a piece of little screw, file it round in about 135 degree angle.


2, remove the bolt and nozzle, drill a hole in a bit of angle for the screw.


3, use a tiny screwdriver, push the floating valve to front(on picture, moving to right), allow space for the screw sitting in between the valve and metal pin but not damage the valve even the pin too.
Now you can see between valve & pin has a gap as the valve is already pushed a bit to front by the screw.


4, screw it all the way in, but be aware to damage the valve if the screw is too long, then shorten it if needed.
Now you may try to screw it back and forth a bit, you'll see the valve moving front and back. The screw adjust turning angle should be within 180 degree to see the result.


5, low fps set up.
Valve is being push the most to the front due to it touchs the higheat side of the screw. Means the shortest traveling distance and get the lower gas flow and fps.

That's test: 0.20gm green gas.


6. Mid fps set up: Turn the screw a big to allow the valve sit back a bit for a bit more air flow, should be around 1/8 turn.

This is the test and raise to gamable fps and maximizethe range.


High fps set up: Turn screw and let valve sit back to normal and have the highest gas flow and fps.

7, the side view from ejection port shows the nozzle sitting in the bolt and the screw for adjust the fps


8, from the bottom view shows the bolt closed.


This modification is working for ghk akm, cause the side of the bolt has a lot of space for the screw.
The other ghk like G5, or Tavor, have to check and see.

Hope it helps whoever would like to make your own Npas for your gbbr. Have fun!