NorthEast FAMAS - Adjustable Rocket Valve

V2 UPDATE: A new design has been created targeting SLA/SLS manufacturing, it restores some geometry from the OEM valve with the goal of strengthening the part while adding some additional material keeping the set screw in place. Obstructions in the bore of the valve have also been minimized, a shorter M3 set screw is now recommended. The old design should work just as well if SLA/SLS printed, and the files are still available under the V1 folder. This new design has been tested and field-proven when printed using SLS Nylon PA12.

Replacement rocket valve for the NorthEast FAMAS (Part no. NGR01NOZ0004), allowing arbitrary energy output adjustment by turning a set screw.

Hardware Required:

• M3 10-12mm set screw (I opted for one with a POM plug to reduce damage to the bolt holding the nozzle assembly together, but this is optional.)

Printing Instructions:

Print in an appropriate orientation with a sufficiently strong material. FDM printing this part is strongly discouraged, it is recommended to use SLA/SLS for this due to the small and delicate nature of the geometry. Make sure the material you use is rigid enough not to deform but strong enough not to shatter on impact with either end of the nozzle assembly.

Regardless of which technique you end up going for, make sure to stress test the part sufficiently before using it in a game, the last thing you'd want to happen if for the valve to break and send your entire magazine's supply of gas down the barrel on a single BB.

Assembly Instructions:

Simply screw in the set screw into the adjustable nozzle. Make sure the set screw can be turned from the front end (the larger diameter hole, opposite of the wider base), which will allow it to be adjusted without having to disassemble the bolt assembly.

After this, disassemble your replica and extract the original rocket valve, replace it with this part and reassemble. Take care when dissassembling the nozzle, the tolerances are VERY tight for some of the parts, so take it slow and don't use excessive force.

How To Adjust Output Energy:

Field strip your replica, and take out the bolt. Insert a thin object through the gas router and wedge it between one of the vent holes, this will prevent the adjustable nozzle from rotating when adjusting. After this, use an appropriate key to turn the set screw either clockwise (reduces output energy) or counter-clockwise (increases output energy). Reassemble your replica, and you should be good to go!

Testing Data:

Using .32g BBs and Swiss Arms Green Gas (130PSI) with an ambient temperature of 25°C, I am able to get muzzle energies ranging at least between ~0.7 J (83.67 m/s) and ~2.2 J (148.32 m/s).

With that said, it should be possible to go even lower, though you may run into reliability issues when tuning it too low. If you want to limit the energy output while not having to extend the set screw too far, you will likely get better mileage by restricting the diameter of the valve by e.g. gluing in a piece of tubing.