A spud gun is a cannon to launch potatoes or other objects with great
speed and over distances of tens or hundreds of
meters. Building and using spud guns is a fine hobby if you are interested
in building stuff or just killing time :)
Most people start with building a combustion launcher which uses an
explosion to propel the projectile. However, if people
get a taste of building spud guns they will usually build more advanced
combustion cannons, or move on to hybrid or pneumatic
cannons. Since spud guns that work with an explosion are classified as a
firearm in Dutch law, I decided to try building a
pneumatic spud gun. I got the required parts from a fellow Dutchman and
built my first pneumatic gun, the NSWP Mk.1
(Nightshade Warrior Pneumatic Mark 1). Below is a picture of my creation:
Following are the parts of my pneumatic spud gun. The part numbers correspond with the numbers in the picture in the picture.
1. Barrel
The barrel holds the projectile that has to be launched. To easily insert
potatoes,
the end of the barrel is chamfered (sharpened). After inserting a
projectile it has to be moved
down the barrel with a ramrod (a simple piece of pvc pipe in this
case).
2. Pressure Chamber
The pressure chamber holds the compressed air. Currently I can pressurise
the chamber
up to 10 bar or 150 psi using a quality bicycle pump. Higher pressures
should be possible
with a compressor or other pressure source.
3. Quick Exhaust Valve
The Quick Exhaust Valve makes it possible to dump air from the Pressure
Chamber very quickly into the barrel. A Quick Exhaust valve has three connections. One
exit (connected to the barrel), one input (connected to the pressure chamber) and the pilot
which is connected to the blowgun. When the pressure chamber is filled and the pilot
is opened, all the air from the chamber will be dumped into the barrel.
4. Blowgun
The blowgun is used for filling the spud gun with compressed air and also
for firing it. For filling the spud gun, the blowgun is opened by pushing the handle
down (or up as in the picture) and securing it with a piece of rope (slightly visible
in the picture). Then the pump has to be connected and pumping can commence :)
5. Bicycle valve
The bicycle valve is used for connecting the pump to the blowgun and
preventing air from leaking from the spud gun while it is filled with air. However, as
most pumps contain an internal check valve this part is not really needed. Later I
will replace the valve with a Schrader valve housing. Still, an extra valve can be a nice
safety feature. As long as the valve is connected, the gun cannot be fired by pressing the
blowgun handle.
To fire the spud gun I first insert a projectile in the barrel, such as
a potato. The sharpened end of the barrel helps cutting the potato into a slug that fits
in the barrel perfectly. Then I push the projectile down in the barrel with a ramrod.
Then I open the blowgun by pressing the handle and securing it with the
piece of rope. After that I connect a quality bicycle pump (SKS AirworX) and start pumping to fill the gun
with air. with this bicycle pump I can fill the spud gun with a pressure of about 10 bars
or 140-150 psi. After filling the gun with air I release the handle of the
blowgun so that the blowgun is closed. Then I remove the bicycle valve.
Now the spud gun is ready for use. When the blowgun handle is pressed, the
projectile will be fired from the barrel with high power and velocity.
Most of the time I use potato's but I also have been working on slugs made out of candle wax or hot melt glue. Details about making projectiles with these materials will be added later on
This is a quite basic spudgun. I decided to skip the usual beginners' ball valve construction because it does not offer much performance. Still, more efficient and powerful guns can be built. The next step is often the use of a piston valve, which can release even more air in a shorter time than a QEV. The QEV concept is still highly recommended for beginners in my opinion. It creates clean designs and is quite simple to build, and has much more efficiency than a ball valve systems.
Spud guns can be quite dangerous if not handled with caution. Projectiles fired from the barrel can easily exceed
the kinetic energy of a airgun or even a firearm. Do not shoot at living things or someone elses property.
Make sure that fired projectiles are stopped by a backstop such as the side of a hill, or just a lot of free range.
Never look into the barrel of a loaded spud gun.
Always use the proper construction materials. When building pneumatic guns of PVC, you have to use pressure rated PVC and fittings!
When PVC explodes it will throw dangerous shrapnel in every direction, so stay within the specified pressure rating of the material.
There is lots of information available on the Internet on building spud guns. Here are a few links to websites about spud guns:
www.uksgc.co.uk