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C:B ratio, call me stupid but...

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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C:B ratio, call me stupid but...

Unread postAuthor: Hillbilly93 » Thu Jan 31, 2013 12:22 am

I understand how to get the volume of both the barrel and chamber, however I'm lost from there. for instance if i have a 2'' barrel that is 60 inches long the volume is 753.6. if i have a 4'' chamber that is 24 inches long i have a volume of 1205.76. but how do i get the ratio from that point?
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 31, 2013 12:48 am

Chamber to Barrel ratio

1205.76 to 753.6

1205.76 : 753.6

(1205.76 / 753.6) : (753.6 / 753.6)

1.6 : 1

Also, you are stupid but :)

(reminds me of that "Call me an ambulance!" joke :D)
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Unread postAuthor: Hillbilly93 » Thu Jan 31, 2013 11:22 am

ty...wow, i don't know why that didn't click in my head.

as far as my stupidity...i was tired when i did that math and i accidently used the diameter instead of the radius.
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Unread postAuthor: Cy4ka » Mon Feb 04, 2013 12:15 pm

Have you used burntlatke's calculator?
http://burntlatke.com/calc.html

Use the "live" ones.
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Unread postAuthor: jimmy101 » Mon Feb 04, 2013 1:36 pm

Hillbilly93 wrote:as far as my stupidity...i was tired when i did that math and i accidently used the diameter instead of the radius.
As long as you are consistent then diameter or radius both work for calculating the CB ratio.

CB Ratio = r<sub>chamber</sub>^2*L<sub>chamber</sub>/r<sub>barrel</sub>^2*L<sub>barrel</sub> = d<sub>chamber</sub>^2*L<sub>chamber</sub>/d<sub>barrel</sub>^2*L<sub>barrel</sub>
(don't need pi either since it cancels out in the ratio anyway)
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Re: C:B ratio, call me stupid but...

Unread postAuthor: SpudMcJim » Sun Jul 07, 2013 1:56 pm

Hillbilly93 wrote:... for instance if i have a 2'' barrel that is 60 inches long the volume is 753.6. if i have a 4'' chamber that is 24 inches long i have a volume of 1205.76.
When you do the ratio, the units of measure don't matter (cancel out). But FWIW, this is what I calculate:

(2.00"/2)^2 * Pi * 60" = 188.5 cuin (3,089 cc) Nominal pipe diameter
(2.05"/2)^2 * Pi * 60" = 198.0 cuin (3,245 cc) Typical pipe ID (Sch 40)

(4.00"/2)^2 * Pi * 24" = 301.6 cuin (4,942 cc) Nominal pipe diameter
(3.99"/2)^2 * Pi * 24" = 300.1 cuin (4,918 cc) Typical pipe ID (Sch 40)

Ratio = 301.6/188.5 = 1.60
Ratio = 300.1/198.0 = 1.52
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