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Custom Gas Gun

This is a failed attempt to create a gas rifle prototype from a cheaply available paintball gun.

Unfortunately it has a number of serious drawbacks, and in the end it just didn’t work out.


I started out wanting to make my own gas rifle. Originally, I wanted to in some way use the gas assembly from a paintball gun (cheap and easily available) and put my own packaging around it.

As it turns out, I wound up using the paintball pistol gun as a base since the gas mechanism is so simple and it seemed a waste to discard the case (which, after all, already FIT the components needed).

The result is what you see here. A stock-less rifle, essentially. It has a custom made magazine as well as hop-up. Not shown is a custom bipod.

It is an insanely powerful gun and is in no way suitable for skirmishing. It is also a failure in my bid to make a usable gas rifle for three big reasons:

  1. It is too powerful and has no way to adjust power.
  2. Inaccurate due to trigger mechanism and internals.
  3. The crude and primitive “regulator” results in very inconsistant shot power.

What I Started Out To Do

I started out wanting to build a small gas rifle (stockless, or folding stock possibly) with sling, bipod, and scope that I could use for accurate distance shooting when the situation demanded it.

I succeeded in the looks and ergonomics (mostly, except for the front handle which sticks out – it contains the magazine) but failed miserably in the rest.

Plus it was a lot of work, despite the fact that you may think it doesn’t look it.

The Problems

The Trigger Pull
The trigger assembly is a very primitive design that has a horribly rough pull. To fire, the trigger disengages a sear that is holding back a spring-loaded weight. This takes considerable pressure to do, and there is absolutely no tactile feedback to let you know if you’re “almost there” or not. So you’re reefing on this bastard of a trigger and it eventually fires. There’s no gradual let-up or anything.

The Regulator / Firing Action
The CO2 (the gun uses 12oz CO2 containers) is regulated (and I use the term loosely) in a very crude manner. Cocking the gun pushes a spring loaded weight back and locks it with a sear (the same one the trigger disengages). At the same time, a spring-loaded valve is opened to allow CO2 to flow into the expansion chamber from the 12oz cartridge in the handle.

To fire, the trigger releases the weight, which flies backward and strikes the valve assembly. The valve is opened, releasing the gas in the chamber.

Why That’s Bad
First of all, the regulator is far from precise. Different amounts of gas from shot to shot means different amount of power behind each shot, which in turn means a different flight path – especially when Hop-Up is used.

Secondly, all these heavy moving parts at the point of firing (actually just *before* firing) means the gun’s going to move and jump when you fire. This has a pretty negative effect on accuracy – which compounds the accuracy problem caused by the ugly trigger pull and the uneven gas loads.

Oh yeah, the high pressures probably aren’t too friendly on the hop-up in the long term, either.

Accuracy Testing

I tested 10 shots at a 120mm diameter target at approx 35 feet with a bench rest and 3x scope with .25g maruzen BBs.

The result is 9 shots in a 60mm group with one deviant out at 85mm (2x 10, 3x 9, 2x 8, 2x 7, 1 outside score ring).

That’d be OK with a pistol, but not with a gun I plan to do sharpshooting with. It won’t get any better than that scoring, and will only get worse as distance increases.

As a side note, the target was on a cardboard box which was in turn filled with flattened boxes. So probably about a half-dozen packed layers of corrugated cardboard. At 35 feet the BBs went RIGHT THROUGH the whole thing and made nice dents in my wall, which I had to fix with poly instafill. Sheesh.

Assembly Pictures and Parts Used

Here is a list of what I used to make this prototype. I certainly don’t recommend you try it since it’s a failure. You’re probably better off modifying a CO2 pellet rifle to accept an AEG barrel if you must try it.

I had to make a few modifications to the case as well as make a lot of custom tubing assemblies for the breech/nozzle/magazine setup.

One more thing: I actually also made a hole and “magazine” for short brass tubes that were ejected just like spent brass casings by some excess gas upon firing. The result was not too reliable, though – so I scrapped it. It was a very cool effect, though. I’ll try to do it again on future custom guns.

Stuff Used:
– 1 Talon Brass Eagle Paintball Marker
– 1 MP5 Hop-Up Unit
– 1 SR-16 inner barrel
– MP5 Nozzle
– EBB Magazine Spring (for custom magazine)
– 3-7x Scope
– Bipod made from a Nintendo Virtual Boy Stand
– PVC adapters, tubes, etc for outer barrel and breech, etc.
– lots of brass tubing, some springs, etc
– resin, epoxy, etc.
– and some misc other parts