Copper Pneumatic Air Cannon

How to create a powerful air cannon from copper pipe and fittings, for very little in the way of cash.

Step 1: Materials

Materials
1.5m (5ft) of copper pipe
One 22mm elbow
Two 22mm endcaps
Two 22mm elbows
One 22mm Ballvalve
One tire valve
Solder
Flux
Ammunition

All pipe in this project can be any diameter, however, as the pipe size increases, so does the bill .
A good chamber:barrel ratio by volume 1:2, however you can change this to suit your needs. A gun with a barrel which is either too long or too short will not be more powerful, but rather less. You can use the Gas Gun Design Tool Tool to find out this length. The ".GDT" file is the saved data for my gun.

As a UK based user getting copper is simple. Many plumbing and hardware stores stock it. I highly reccomend BES Gas and plumbing supplies. I suspect the situation is similar in the US. Ballvalves are very common, and can be bought from most plumbing stores.
Flux and solder will more than likely be available in the same store.
A tire valve can be got from any auto store, or ebay. I got 10 snap in tire valves off ebay for �3 posted. nd they are perfect for this project.

Step 2: Tools

Tools
A vice (and bench)
A powerdrill
A file or debrring tool
A pipe cutter
or A hacksaw. (If you are using a saw you will need a miter block)
A blowtorch and lighter
Old gloves, these will need to insulate you from hot pipe
An old newspaper, this will protect yor work surface and insulate you from hot pipe.
Wet + Dry paper (a fine form of sandpaper)
A drillbit (for a standard schrader valve you will need a 5/16)
A fairly large spanner - My adjustable one was too small. I used a mole grip and wish I'd looked for a proper spanner.
A bike pump, for your valve.

Step 3: Preparation

As you have probably noticed my gun as a single strip of chamber, with 2 "branches" to stabilize it. It is an over-under design. The total length of your stabilisers will need to be a bit longer than your upright bit. The longer the stabilisers are, the more stable your gun will be.
A good chamber:barrel ratio by volume 1:2, however you can change this to suit your needs. A gun with a barrel which is either too long or too short will not be more powerful, but rather less. Don't forget to include all the pipe including the stabilisers in your volume estimation.
You can use the Gas Gun Design Tool Tool to find out this length. The ".GDT" file is the saved data for my gun.
After you have cut the pipe to the size you want , you must remove the burrs, as these will hinder your soldering. The cut needs to be clean and straight.

Step 4: Adding the Valve

You will need to fill the chamber somehow. To do this you drill a hole in the endcap and glue in the valve. Mark the center of the endcap and clamp it in a vice. Get your drill. A standard schrader valve is around 5/16", but the hole will need to be a little larger if you're using a snap in valve. Save yourself some time and make sure you use a power drill and vice.

Step 5: Soldering

This is the hardest part.

1/ Solder works best if both the pipe and the fitting are really clean. Use fine wet and dry or wire wool to get all the surfaces shining.

2/ Flux should be applied to both the end of the pipe and to the inside of the fitting. Use a brush, flux is nasty stuff it rots skin and once its on your hands you will get it every where and that’s how you pipe starts to go green. All you need is a thin coating, think of how thick lipstick goes on and that’s about what we are after. To be honest we are talking about a strippers lipstick but you get the idea.

3/ Assemble the parts to be soldered. Remember for really strong joints you want to solder all of them at once. You may need to rig up a bit of a jig to hold everything straight and true but stay calm you can take ages over this bit the flux won’t go off. This is a good time to recommend the brand of flux I use, its called EverFlux and I use it because it isn’t active until you heat it, this is important if you might want to adjust stuff a few time before you solder as active fluxes will make fitting and pipe stick together in a few minutes.

4/ Solder is drawn towards the heat if you have to solder an elbow with one joint pointing down its Ok just do the other joint first and the heat will help with the difficult one. Heat the pipe first, do this until you just see it change colour, this takes a few seconds maybe 10 with 15mm and progressively longer as you use larger pipe. Now heat the area just beyond the joint, for instance on an elbow heat the bend. Again wait for the colour change and apply solder opposite where you are heating, you should see it melt and be draw into the joint. Don’t use too much solder you want to be aiming to use a similar length to the diameter of the pipe you are using as a maximum. More solder wont help it just falls into the fitting and starts to block it up. Now heat the other piece of pipe in you fitting and then back to the middle and again with the solder.

5/ LET IT COOL DOWN!! Only cowboys use a wet rag to cool pipes, don’t rush it.

6/ Clean your joints, if you can clean the inside as well. You don’t want all that nasty green stuff everywhere.

7/ If in you don't feel confident try using solder ring or Yorkshire fittings, the flux bit is the same but you don’t need to add solder. Heat a little above the joint line until you see solder all round and then stop.
Credit to Cornishtiger of The UK Spudgun Community (who is a professional plumber) for the excellent soldering guide.

Step 6: Adding the Valve

The valve will be a compression fitting. Put the pipe into the correct valve port and tighten it. The olive (metal ring inside) will compress around the pipe meaning it won't move. This will form a seal.

Step 7: Fire!

My favourite ammunition for a 22mm barrel is an empty 12g CO2 cartridge. But you can use anything which fits in the barrel. Close the ball valve, pump it up and release the valve. Power will change depending on how big you made your gun. The faster you open your valve, the better your shot will be. Pumping your gun with the valve open results in cool compression condensation rings. Have Fun! and be safe.

There are several places to find out more across the web.
*UKSGC
*Spudtech
*Spudfiles
Are probably the 3 largest