Making a Paintball Gun From Scratch – Hey! It's a Gun!

With our last build resulting in a gun that could be muzzle loaded to fire single shots, Brian was confident that we could attain semi-auto firing over the course of the coming weekend. The main problems and parts that needed to be addressed to get to that point were correcting the cycling issues in the bolt, rigging a sort of makeshift trigger system to fire the gun, and feeding paintballs into the system.

The issue that had to be solved first was the issue of cycling. After our second build, we found that the bolt was not being forced forward by the firing pressure when the control pressure was released. To fire the gun, we had to assist the bolt by pushing on the back of it with something. We expected that the primary cause of this problematic friction was the surface finish of our internal parts. This appeared to be an easy fix after some fine grit sanding on the lathe. Another way that we helped the movement of the bolt was by deepening the o-ring grooves to relieve a little pressure on the bolt.

After these two fixes, the bolt started to cycle the way it was intended. In order to achieve semi-automatic dryfiring, we had to rig up a hose system to imitate our future trigger. This is roughly what we came up with…

Gun air rig sketch semiauto

In this setup, pressure is supplied by separate hoses. The firing pressure is constant as it will be on the final version, and an air gun is used to dump pressure from the control chamber in place of a solenoid-actuated valve. We did have a problem off the start because the trigger pressure input was pumping air too fast for the air gun to dump it. this was causing the chamber to remain at too high a pressure for the bolt to cycle. to fix this, we basically jammed a plug into the input hose to slow the rate at which air could flow through it just enough to allow the bolt to cycle. With this setup, we achieved semiautomatic fire without ammunition.


At this point I am returning to this post after over a year of absence, so my recollection may be a bit fuzzy. I apologize for any inconvenience.


In order to feed paintballs into the gun, we decided to create a basic hopper feed system by boring a large hole in the top of the gun. We then threaded the hole and created another piece that fit tightly onto the neck of a hopper and threaded into place on the gun.

Since this was the first time we had to do anything on a different axis than the firing axis, it meant we got to use a new toy. Brian had recently bought a four jaw chuck that was useful for this type of operation. The mount for this job is pictured below. The hole was started using a wood bore bit, and the hole was widened using a boring bar.

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After making both parts, we attached a hopper and voila! It is amazing how much that hopper makes it look like a gun.

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We rigged up our makeshift trigger system (partially pictured above) and took it outside to try firing it a few times.

Now that the firing mechanism is operational, we need to set up a trigger mechanism. The primary phase of this process will be the design of the solenoid valve. A concept is shown below.

First: A cross-section of the valve                     Second: A full image of the valve hammer



This valve will be actuated like a solenoid. There will be a copper wire winding around the left end of the valve body which will pull the hammer back when charged.

In the rest state, pressure will be routed through the valve as such:

Valve_clip_air_diagram_restWith the valve in its rest state, constant pressure is applied to both the control chamber and the firing chamber. Due to the pressure in the control chamber, the gun does not fire. Once the valve is actuated by an electric current through the solenoid, the air pressure will behave as such:

Valve_clip_air_diagram_fireWith the control pressure now dumped, the present firing pressure will be able to fire the weapon. After firing, the source pressure will return the hammer to its original position as soon as the solenoid is deactivated, allowing the recharge of the control chamber.

Hopefully with some refinements to this design, and a free weekend to build, Brian and I can get a real paintball gun together. We still have to deal with making the gun run on CO2, which brings in a whole host of regulation and expansion issues, but I think we are fairly close to a workable product.

I am sorry to anyone who was affected by my delay in posting this write-up, and I hope you enjoy its contents.