SpudFiles

That picture was taken right after I got all the stuff put on, so it's not quite "finished".
This gun has a 24in long 4in diameter cumbustion chamber. The fuel is metered propane, but I am going to be using MAPP in the spring. The ignition is dual sparks from a 600K volt stun gun (gutted, and placed in a case for easier access to batteries). Two bolts are run through the chamber (one about 1/3 down the chamber, the other 2/3), and there is a piece of 1/2in PVC I cut down the center on the inside of the chamber, and in that I mounted 2 more bolts that are connected with a wire (kinda like a spark strip).
The barrel I use is 2in by about 5 foot long. This is used for spuds and golf balls, with a sabot. For a sabot I use either paper towel, or caps off of aerosole cans. (Since I have Banjo fittings for the barrel now, I can use burst discs.)

Upgrades I have done include Banjo fittings to remove the barrel faster. I replaced the end cap with a 4inch male fitting, with a 2inch ball valve. I am adding a chamber fan to it, which has a timer circuit connected so it will run about 20 seconds by pressing a button. The propane meter is mounted a lot nicer now, no bungee cords. I converted the gun to an over/under, since it was too long. That was done by adding a 3inch street and 3inch 90degree with a male on one end and a female on the other.

Holy ravioli! That thing has 3inch fittings for removable barrels? Huge! I like it, a lot!

I like it too. It's very clean. I like guns with everything you need onboard.

I like you loafers. Look a little like mine.

Heh heh... just kidding. Nice cannon!

Yes, those are 3inch fittings for barrels. I figured they would flow better than 2s, and 4s just wouldn't look good. I wanted to use 6inch for the chamber, but I didn't like the selection of fittings and the cost of them, and the pipe.
It's not even completely done. I still haven't put the chamber fan with timer circuit on (its just like the one on this site http://www.burntlatke.com/fan-controller.html), and I plan to put that in a new box along with the ignition, which I plan to add a nicer switch to. The case I have now is handy, but it just doesn't look very good.

I can honestly say I'm not even sure how much the gun costed, but heres a guess.
4inch pipe was maybe probably $15 for the 10ft
3inch I had lying around, (same with 2 for the barrel)
fittings...a guess would be about $40? to date
Banjo fittings, I believe $25 or so for the set of 3inch
stun gun, about $25 (eBay)
propane injection about $25
Fan controller timer, about $10 with a salvaged fan from an old computer power supply and other salvaged components, plus time and lots of solder and wire.

EDIT: It looks clean mostly since I used clear primer. I actually slopped a little on the cannon while assembling.

One of my dads friends from work wanted me to build him a gun after hearing about this one. I turned it down, only because I was so busy with my crappy job (which I later quit). This cannon was actually made over the period of about a month gathering materials, cutting, and finding time between work and other BS that was going on.

So, would it be safe to use a 1inch barrel on this? What about with a burst disc?
I want to see how far I can possibly shoot with it. So I figure a smaller barrel would give me higher velocities hopefully, the gas has to flow through a smaller opening and thus at a higher speed. And of course a burst disc would have to help.

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I usually shoot golf balls and spuds. What would you suggest as a projectile?
I have some lead, but I don't feel like casting that. Metal pipe filled with rocks may be a possibility.

It will be warm this weekend, about 50, so I may attempt this pretty soon. I'm thinking burst discs, and some kind of saboted projectile. I will look around later and find stuff.