C:B ratio

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Postby dionysos » Thu Feb 01, 2007 11:15 pm

Hello, I know that this subject has been brought up before, but I was not able to find it with a search. I am confused about the C:B ratio for a combustion gun. The theory page states that 1.5:1 is the best ratio for a spud gun, but then I have seen .8:1 in the forums as well. Which is it? I will be using Right Guard, with a 1.5" diameter barrel. I made one cannon with a 2" diameter barrel, but was not happy with it, as many of the potatoes were too small to give a good fit. With a 1.5" barrel, what would be a good (proven) size combustion chamber to use? I Have both 4" and 3" on hand.

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Postby noname » Fri Feb 02, 2007 12:07 am

Right Guard no longer works, unless you're using the kind that's over 8 years old. Try hairspray. AS for the C:B ratio, .8:1 refers to propane cannons, while 1.5:1 refers to the type of fuel fro a cannon like the one you're building.
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Postby SpudBlaster15 » Fri Feb 02, 2007 3:10 am

Right Guard still works, a local drugstore just received an order containing around 30 cans of it, with main ingrediants being butane, propane, and isobutane.

A 1:1 ratio works well for a cannon of this type. A 1.5:1 ratio wastes alot of energy, even if you are using an aerosol fuel.
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Postby FLONE » Fri Feb 02, 2007 9:47 am

My 4" x 10" with a 1.5" x 46" barrel is a bit on the loud side, but it does fit in the trunk of the car. Portable. I would choose a 60" barrel if I was redoing it. Static Guard is a bit pricey, but it will not disappoint. OUST works well, nice flames with low power loads.
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Postby jimmy » Fri Feb 02, 2007 1:14 pm

Any C:B ratio in the range of about 0.5 to 1.0 will be fine. If you look at Latke's C:B studies (<A href="http://www.burntlatke.com/15cb.html">here</a> and <a href="http://www.burntlatke.com/jpg600/15cb-graph.gif">here</a>) there is really very little change in muzzle velocities over that range.

A C:B of 1.5 will suck (or blow?).
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Postby An Apple Pie » Fri Feb 02, 2007 4:42 pm

1.5:1 is good for sound, but .8:1 is the most efficient. Do not use hairspray. It is not near as powerful as right guard. It gums up your chamber, and I also beleive that it is more expensive.
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Postby Arborman495 » Fri Feb 02, 2007 7:50 pm

NEVER USE HAIRSPRAY!!!! It will gum up your chamber and it is one of the LEAST powerful fuels. Axe works fairly well. Right Guard DID change so that it NO LONGER WORKS, but the long supply chain of many stores still has the good stuff. Use Static Guard. This comes in a skinny can with an orange cap. This is one of the best. Way better than good Right Guard.

As for the ratio, I prefer 1.5:1 C:B. This does have some noise to it, but I dont like guns that are too quiet. Other ratios do work better for efficiency and stuf like that. When I am going for quiet, I choose a pnuematic.

My Pnuematic, which is a product of the "quiet tree entry pnuematic topic", is very similar to this http://www.antennalaunchers.com/csv19/index.html It works fine. I used converters insted of endcaps and 2" barrel instead of 2.5"
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Postby larryb » Sun Mar 04, 2007 1:56 pm

Try looking at the following link for fuel tests and chamber pressures done by spudgun.com website.


Larry B
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