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Noob Spud Gun Questions

A place to ask general spud cannon related questions.
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Noob Spud Gun Questions

Unread postAuthor: niceguyjps131 » Wed May 18, 2005 1:56 pm

I have been making potato guns for about 1 year now(Built 2 guns), which is a long time to me, but im sure theres people with alot more experience. For the past year i have been getting my info from what little web pages I can, until I found this forum. I was hoping someone could answer some quick questions for me.

1.) I am planning on building a new gun with detachable barrel out of 4in PVC for the combustion Chamber and 2in for the barrel. I wouuld like it to be 8 feet tall or taller . Can someone tell me the optimal ratio in feet to make the combustion chamber and barrel?

2.) Does anyone know or have some drawings on how to make a bipod or stand for my spud gun out of PVC?

3.) Also What is a burst disk and how does it work. I would just like to have more niose from my spud gun.

Thanks
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Unread postAuthor: spudshot » Wed May 18, 2005 5:08 pm

1. you want a 1.5:1 C:B ratio for aerosol and about a .8:1 ratio for metered propane
2. all you need to do is cut 2 pieces of wood that would make the barrel stand at optimal hight, and a cross bar between them for support, then attatch the top of the legs to a hose clamp and tighten the hose clamp around the barrel
3. a burst disk is a piece of aluminum foil or other material that is sandwitched between the 2 pieces of a union, then when your gun fires it will rupture when enough pressure is behind it (you dont want to thick of a burst disk because it might cause the cleanout cap to blow if its too strong)
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Unread postAuthor: milty » Thu May 19, 2005 5:43 pm

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Unread postAuthor: boilingleadbath » Fri May 20, 2005 2:14 pm

Now... Stop being silly! There is no fixed optimum ratio! There is a best barrel length for a chamber, but if your building both... Let's just say it doesn't exist!

What I'd recommend doing is downloading the GGDT, and use the overall gun length optimization tool once you'v figured out your combustion results. (use a fast generic valve with a very high flow coefishent). This resulted in 1.5:1 for a propane (if I remember right) launcher where the chamber was twice the diameter of the barrel. (just like your 2" and 4")

Unless you make an over-under... then it matters not - a bigger chamber will not make your total length longer, so the length of the barrel (8 feet!) is the limmet.

If you want it to be quiet, however, ignore the above post - the standard ratios use all the availabel pressure so you don't got the loud excape of super-sonic gases.
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Unread postAuthor: spudshot » Fri May 20, 2005 2:52 pm

boiling, how the hell would you get an accurate reading using GGDT, a tool designed for pneumatics?
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