Multi-Barrel Air Cannon

 Check out this sweet gun with interchangeable barrels.
I built this on my own but I used plans for the kits here at 
http://jjincorperated.weebly.com/air-gun-order-form.html

Step 1 Build The Tank N' Such

 You will need:
24" of 4" PVC
4" End Cap
2 X 4" Elbows Male-Female
4"-3" Reducer
3"-2" Reducer
2" PVC Thread Converter
2" Threaded Valve

Assemble like the fallowing picture.

Comments

[BluesBrother]

How do you pressurize it?

[jj.inc]

There is a quick-connect part that we added so it hooks to our compressor and fills much faster than a schrader valve (like the one on your tires). but if you are planning to do this with a hand pump, I definitely recommend halving the size of the pressure chamber because this takes time to fill up with a 100 psi compressor (yes it is more than big enough) through a good 1/4 inch size hole. But if you have a half hour to get some exercise, this would be great.

[BluesBrother]

How much would a compressor cost? Might need the workout anyways.

[jj.inc]

Well, your looking at about 300 dollars for one that can sustain three to four shots before giving it about a minute to pump up (we have this).

You can get a huge one like this which will keep it sustained for infinite shots as fast as you can shoot, close, fill, and reload. (don't recommend it, its excessive.)
http://www.csnstores.com/asp/superbrowse.asp?clid=766&caid=&sku=IRC1201&refid=FR49-IRC1201

or a small one like this and just add some large PVC tanks for more air (buy two or three entire pieces of PVC pipe, what are they, 10 feet? and then just cap one and add the required fittings.)
http://www.amazon.com/Campbell-Hausfeld-FP2028-Compressor-Accessory/dp/B000BOCBAM

You can also get expansion tanks here: http://www.mcmaster.com/#pneumatic-tanks/=bysvdh

The portables are nice because you can fill them and then go somewhere, or something along those lines. Even if you aren't going anywhere, they still look a little more cost effective.

Easiest thing to do is start searching google shopping for the best deals, just drop your price on the side to what you are willing to pay.

[m0f0]

It'd be nice if you showed how to do it with te tire valve

[jj.inc]

just replace the air compressor attachment with a shrader valve.

[Lance Mt.]

 I like the pressurized rounded tube design 

[jj.inc]

 If I know what your talking about (the curved under over style) then yes it is a very nice design, it helps allot with support and space