How do i calculate a c:b ratio?

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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spudkilla
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Sun Feb 11, 2007 6:00 pm

I am building a combustion cannon (hopefully fairly large 7-10 feet long)and I was wondering how long should the chamber be( 3 inch in diameter),and how long my barrel should be(1.5 inches in diameter)?I all ready searched, but i got nothing.
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crazyfreak0075
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Sun Feb 11, 2007 6:09 pm

Im assuming u know how to use proportions but a .6-.8:1, C:B ratio is about right for a combustion cannon. Its all here in the wiki http://www.spudfiles.com/spud_wiki/inde ... rrel_ratio
SpudBlaster15
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Sun Feb 11, 2007 7:16 pm

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Last edited by SpudBlaster15 on Wed Jul 14, 2021 1:13 pm, edited 1 time in total.
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spudkilla
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Sun Feb 11, 2007 7:42 pm

Oh, i almost forgot..ill be using aerosol flammable fuels
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spudkilla
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Sun Feb 11, 2007 7:48 pm

Wait could i just double or triple or whatever the lengths on here to make it the size i want? http://www.spudtech.com/content.asp?id=5
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willarddaniels
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Sun Feb 11, 2007 9:55 pm

No, those are generic instructions. You should calculate the volume of both your chamber and the volume of your barrel, then use the ratios suggested by CrazyFreak. Typically, (.8-.95)Barrel:(1)Chamber

Start with your chamber. If it is 3" ID, and the length is 24", your volume would roughly be 168 cubic inches.
Your barrel should be 80-95% of that volume: 134-160 or 76-90 inches long, asssuming 1.5" ID barrel. That is a total length of 100-114 inches, not including space for a reducer.

Do not use these exact numbers for your gun, but use them as a template
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Sun Feb 11, 2007 10:19 pm

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nec placerat erat. Vivamus dapibus egestas nunc, at eleifend neque. Suspendisse potenti. Sed dictum lacus eu nisl pretium vehicula. Ut faucibus hendrerit nisi. Integer ultricies orci eu ultrices malesuada. Fusce id mauris risus. Suspendisse finibus ligula et nisl rutrum efficitur. Vestibulum posuere erat pellentesque ornare venenatis. Integer commodo fermentum tortor in pharetra. Proin scelerisque consectetur posuere. Vestibulum molestie augue ac nibh feugiat scelerisque. Sed aliquet a nunc in mattis.
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