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Barrel to chamber size?

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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Barrel to chamber size?

Unread postAuthor: KS-collector » Thu Sep 22, 2011 3:44 pm

Im no math wiz, so can anyone double check this ratio for me? Barrel is 3 inches wide, 3 ft long. Chamber is 6 inches wide, 15 inches long. That should be about 1:1.5 barrel:chamber ratio, correct? Which is the proper ratio, yes?
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Unread postAuthor: ramses » Thu Sep 22, 2011 3:46 pm

I got 1:1.666 B:C
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Unread postAuthor: KS-collector » Thu Sep 22, 2011 3:52 pm

Close enough to 1:1.5 for me. Thanks!
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Unread postAuthor: jsefcik » Thu Sep 22, 2011 4:10 pm

What ever your chamber is make your barrel double your chamber size!!
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Unread postAuthor: KS-collector » Thu Sep 22, 2011 4:22 pm

jsefcik wrote:What ever your chamber is make your barrel double your chamber size!!


But I thought the chamber had to be bigger to propell the spud (or in my case nerf football) all the way out of the barrel. If I could make the chamber smaller, it would greatly help my purposes but I dont see how that would work as well as a large chamber even accounting for expansion of ignition.
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Unread postAuthor: jsefcik » Thu Sep 22, 2011 4:35 pm

If your chamber is too big and barrel is short your not getting full potential out of your gun

For example 3 foot chamber to a 6 foot barrel , you want your gases to fully burn!

If you can't get the barrel and chamber ratio right you want it close as possible

My piston cannon has a 5 foot barrel and chamber
My barrel should be longer but I'm not made of money !! My pistOn cannon puts golfballs 500 yards and beyond

Pm me if you want
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Unread postAuthor: ramses » Thu Sep 22, 2011 5:11 pm

For a given chamber volume, the optimal barrel will be 1.4x bigger than the chamber. Any bigger, and you start to loose performance.

With a constant barrel volume, the results are more complex. This shows that anything above 1.2 hurts performance, but HGDT predicts a steady increase
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Unread postAuthor: mattyzip77 » Thu Sep 22, 2011 5:51 pm

The wiki knows all!! Also, look at other members c b ratio. I would say your close enough. Also try running different figures through GGDT. Welcome and good luck!!
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