NA-4 Bullpup Airsoft Gun

A custom HPA airsoft rifle that uses M4 magazines. I designed this to be comfortable, short, and light. I am told it is akin to a P90, however the Magpul PDR-C is far closer in design to this gun.

I also made this gun capable of fitting inside a 53cm long fishing case which is available on Amazon or Ali-Express. Included is a photo of an earlier model inside a case.

Requires:

• Polarstar Kythera engine
• Air line for Kythera
• Hop-up with a round dial
• 300mm barrel (can be longer but will stick into silencer)
• Maxx Model CNC Aluminum Advanced Magazine Release - Style A
• Silencer foam from Ali-Express, 100mm long. Look for Internal Spring Foam Airsoft Suppressor.
• 256mm long Weaver Rail from Ali-Express
• 1/2" diameter stainless tubing, 1/16" wall, 11.7" long
• 6x 1/8" diameter, 1/2" long dowel pins
• 6x 1/4-20 x .88 SHCS-ZN bolt
• 6x 1/4-20 Nut-ZN
  -1x 8-32x.75 SHCS
  -1x 8-32 Nut
• 6x 1/4" diameter, 1-1/8" long clevis pin (McMaster Carr 90156A506)
  -2x 3/16" diameter, 1-1/2" long clevis pin (McMaster Carr 90156A502)
  -.09"dia weld rod, 25" long. May be able to use a coat hanger

The photos show how the gun is put together.

The metal rod that connects the trigger to the Kythera is made from weld rod. I assume a coat hanger would work here as well. The rod is bent into a C shape with the long sides 11-3/16" from rod center to rod center.

An 8-32 bolt and nut is used in the Trigger Pull. This is used to push on the Kythera lever. This bolt should be tightly secured. Washers may be required to get the optimal distance.

Issues I had and solutions:

Trigger does not pull
The safety may be in the way. You may have to carve some of the safety block out so that the trigger can be slid forward.

Kythera not firing after one successful shot.
This can happen due to the trigger not returning to home and the Kythera not resetting. To fix this, the #8-32 screw must be set to a further distance back on the Trigger Pull. Other causes would be the metal connecting rod between the Trigger and Trigger Pull is rubbing on the walls of the housing. Either carve out the plastic so the rod can move freely or make a new rod.

• Magazine Release not holding the Magazine
  The magazine release has a piece of metal that can be removed to lower the magazine release and allow different shaped magazines to fit inside. As well, ensure the support material around the magazine release is not binding the locking mechanism.

-Gun is not firing after a good few hours of working
The 8-32 bolt on the Trigger Pull has been noted to loosen with time. I have needed to locktite this in tightly and use washers to hold it in place. Tightening the bolt will bring the gun back in to working order.

If you have questions about assembly, ask and I will try to answer as needed.

If you wish to make a donation, you can purchase this from my Cults3D
https://cults3d.com/en/3d-model/game/na-4-airsoft-rifle