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Building a big cannon. I need advice so I can do it right

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Building a big cannon. I need advice so I can do it right

Unread postAuthor: AgiTator » Wed Sep 17, 2008 9:36 pm

At the moment, I'm a happy spudder. I have a cannon with a 2" x 6' barrel and a 4" x 16" chamber. It's a spray and pray with a single gap ignition. I've experimented with different fuels and love propane. Though I'm happy with this gun, I want to build a bigger one and have for a long time.

I've been dreaming about building one out of 6" pvc for the chamber and 2" or 3" pvc for the barrel. I have never seen 6" pvc in hardware stores, but I have been to a plastic pipe industrial store. They sell all the stuff I could ever dream of needing. So- I can get/afford the materials.

I watched this video and liked it a lot. I would like to build something similar or identical.

http://www.youtube.com/watch?v=sdFK5eVm ... re=related

My plan was to do spray and pray, maybe metered propane if I feel like it. As far as ignition, I was going to do a multiple gap barbecue ignition. I would also like to build some kind of shield around the gun in case the pvc lets go... that way I'm less likely to die if something breaks.

I would love to hear some thoughts on the 6" pvc pipe. Has anyone here built something like that? Have you had trouble with it breaking?

I'd rather think everything through now instead of just impulsively building something that will fail or break, etc...

Any help is appreciated...

Thanks

~Tator
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Unread postAuthor: AgiTator » Thu Sep 18, 2008 5:07 pm

Another thing...

I would consider using 8" pvc for the chamber.

I can't decide whether to do an over-under or an inline. Inline would probably get bulky with something that big. Then again, I like the look of an inline better. THe over-under would be easier to fuel and load. You could just stand it on its end and load it, then spray fuel in the front end of the chamber.

I want a barrel that fits a lot of types of food cans, so I'm in the process of measuring different canned goods, ha ha.
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Unread postAuthor: iisthemuffin » Thu Sep 18, 2008 6:38 pm

For furture reference, edit instead of double posting.

I have not built a cannon this large but i would not recommend making it a spray and pray. That would be a waste of so much potential.

I would say metered propanne. And it may be hard to find 8 inch PVC that you would be "safe" in using.

Six would be a little easier but would still cost you a pretty penny. If you have a freind or can get a hold of someone that works in a factory that makes drinks then you can get a hold of some pretty massive pipes. Especially at a brewery.
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Unread postAuthor: starman » Thu Sep 18, 2008 6:39 pm

You can get 6" PVC at commercial plumbing supply stores. Most of the 6" you see at Lowes is cell core. Find the place in town where the construction and industrial contractors buy their plumbing. That's the place to go. You will probably have to purchase a 20' piece though. Take a handsaw with you in your pickup truck so you can saw it in half.

Since you've already built a successful spray and pray, you should consider making this one an advanced model with metered propane and a mix fan(s)... 2 or 3 spark gaps and a stun gun ignition.

I'm an inline guy and a gun this large would just about have to be mounted anyway. If you are planning to shoot veggie cans, recoil from this thing will be significant so take that into account when fashioning handles and gun mounts.

Good luck with your next gun!!

Edit: Oh yes, if you use your materials properly you won't have to worry about building a "shield"....unless you just want to of course.
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Unread postAuthor: AgiTator » Thu Sep 18, 2008 7:52 pm

Thanks for all the info!
I usually do edit my posts instead of adding another, but I was having computer problems the other day.

I will definitely use pressure rated pvc. As far as buying it, I am in the industrial field and have some good connections (no pun intended). I probably won't end up buying a whole 20' length.

I'm leaning towards the over-under style gun. I might even just duplicate some of the dimensions of the one in the video I posted.

Metered propane is appealing and then you can have the tank strapped to the gun instead of carrying a can of stuff around. The stun gun ignition does sound good but then you have to charge it and have a battery. I'd love to discuss it some more.

I can get my hands on a ton of those computer fans (brushless) for circulation. That shouldn't be a problem.

I do have confidence in my construction/cementing skills since my last four builds have never exploded. However, it will help my peace of mind if I have some kind of protector. I'll think of something I can put between myself and the chamber. On my inline, I took some larger pipe and slit it, removed a slice and then hose clamped it over the entire chamber. It's probably not necessary, but I like having it.

The recoil thing has been on my mind. I want this thing to be as big as possible but still carry-able. I'll make it such that I can rest the end on the ground while firing. I don't mind having a big gun though- I'm 6'7" and 225 lbs. I want something with a little kick.

Suggestions on barrel size are much appreciated. I'm considering having a threaded coupling at the end of the chamber so that I can interchange barrels... that way, I could get some 2.5" pipe for tennis balls, 3" for canned goods and 4" for large canned goods. I think it'd be hard to run a 4" barrel with a 6" chamber. I haven't looked at the calculation charts yet though. I have some math to do. I'm leaning towards using 8" pipe for the chamber and having it about 4' long.

Anyway... I appreciate the info and I'll continue with my research. I've been searching the site for some time already and found lots of good stuff. Though I love pneumatic, this thing has to be combustion... I love stuff that burns and makes the loud bang. I also hate having to use a compressor or pump things up with the bicycle, blah blah...

Thanks again

Tator
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Unread postAuthor: brogdenlaxmiddie » Thu Sep 18, 2008 8:30 pm

Damn, That's gonna be a [female doggy] to carry around... Even for someone of your stature. I would recommend doing a over-under, or you could go Halo style and do something like a brute shot and have a pansersheik style guard on the front. Gimme a while and I'll find a pic of what I mean...

Ok- So I couldn't find a pic of the gun in Halo I was thinking of.. But here's another one- http://world.guns.ru/machine/dshk_001.jpg
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Unread postAuthor: AgiTator » Thu Sep 18, 2008 9:36 pm

Ha ha! nice picture.

Whatever size I choose, I'll weigh the materials and make sure it's reasonable. I expect it'll weigh an amount which is similar to the one in the above video. That one is claimed to weigh 10kg which is about 23lbs. I may be wrong. It definitely won't be something that i'll take on hiking trips, lmao.


Do you guys know if the two 90 degree fittings used to turn the corner for the barrel will restrict the expanding gases in any significant way?

I've been reading up about ignition and chamber volume.

Thanks

Tator
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Unread postAuthor: FLONE » Tue Oct 07, 2008 12:30 am

AgiTator wrote:Do you guys know if the two 90 degree fittings used to turn the corner for the barrel will restrict the expanding gases in any significant way?


How much is significant? How can it be satisfactorily measured?

If you are thinking of using a 4" barrel then you would probably use a pair of 4" elbows. Take a gander at how far that places the barrel off the chamber. Considering the weight of the barrel and the leverage exerted on the elbows and the joints, perhaps an inline style should be considered.

And a 6" chamber with the cleanout and front bushing plus connector will weigh a bunch, Yup, you are a big guy, but the recoil will surprise you.

I like Jimmy's idea of sparks placed at intervals of a chamber diameter apart. Check out his ideas on that.

Perhaps a pair of 80 mm fans mounted side by side or a single 120 mm will keep things moving inside the chamber.

Good luck and keep us posted.
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