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C:B Ratio

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C:B Ratio

Unread postAuthor: Lucas_Pukas » Wed Feb 01, 2006 2:27 am

So I have searched all over looking for information on the C:B ratio, but I can't seem to find anything that will help. Maybe I'm just thinking too hard...who knows. Anyway, if someone could even just point me in the direction of which forum I could find the info in, that would be awesome. I have a 12" chamber with a 3' barrel. Thanks a bunch.
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Unread postAuthor: Rambo » Wed Feb 01, 2006 8:48 am

Teoratictloy if we don't count the friction and the cooling of the gases the most eficiant ratio is C:B 0,5:1 I suppouse it is also noiseless.
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Unread postAuthor: boilingleadbath » Wed Feb 01, 2006 4:42 pm

Where'd you get that idea, Rambo?

First off, let me note that cooling of the gasses doesn't seem to affect the data much (I'v concluded that the variation in the latke data is due to the different sectional densities of the projectiles, because it correlates so well with that), and the GGDT indicates that even large differences in friction change the velocity very little.

As the the origional question:
<a href="http://www.burntlatke.com/launch.html">Acctual tests</a> have been preformed by Burnt Latke. They all converge on the same ratio for full utilization of provided pressure.
And yes, at said ratio, it is very quiet.
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Unread postAuthor: cardinals08 » Wed Feb 01, 2006 6:31 pm

isnt it 1.5:1 C:B ratio? what rambo said would mean the barrel is 2 times larger than the chamber
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Unread postAuthor: CS » Wed Feb 01, 2006 6:45 pm

He said effeint, not most powerful. Because obviously the larger chamber to more powerful, but when the chamber side of the ratio starts getting larger then that of the barrel, lots of energy goes to waste from the combustion. So at the "most effient ratio" the force from the combustion will be all (or almost) used. If you go to low the force from the combustion will be exhausted and your effeincy will go down.

Im not sure to if it is the most effeint ratio, but thats what he is claiming. 1.5:1 is typically suggested for aersol powered combustions while .8:1 is suggested for propane metered combustions. (Just in case you were confused to where all the different ratios were coming from)
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Unread postAuthor: Lucas_Pukas » Wed Feb 01, 2006 6:46 pm

So if my calculations are correct, the volume of my barrel is 113.0973355 in and the volume of my chamber is 56.54866776 in. With those numbers, it seems my C:B ratio is .5:1. Unfortunatly, that is a different ratio than the ideal 1.5:1...But I haven't had any trouble with it. Is it worth trying to change it, or would that be too much trouble?
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Unread postAuthor: boilingleadbath » Wed Feb 01, 2006 8:21 pm

Many people don't think the 1.5:1 ratio for aersol fuel guns is correct... and I'm one of them - it's the same fuel, for goodness sakes, although the precision of the mix isn't as good.
Damn you, Joel, for perpetuating that myth. Even once we get acctual data on it, it could take <i>years</i>, if not <i>decades</i> to correct the popular oppinion.

As to correcting the ratio, you could cut you barrel to 65% of it's current length, for a .7:1 ratio - your barrel is so long that it's starting to slow the projectile down. (shortening it will make it a bit louder, but .7:1 is still pretty quiet.)

Oh, and watch that precision. They don't make measuring devices accurate enough for you to know your lengths to anywhere near 1/100000000", and you personaly probably don't even know it to 1/100" - infact, you may be using the nominal diameter of the pipe instead of the acctual value, which can induce inaccuracies of several percent.
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