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C:B for a pneumatic

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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C:B for a pneumatic

Unread postAuthor: Rambo » Tue Feb 14, 2006 5:01 pm

I'm building a self recharjing pneumatic and I want to know what is there big diferense if the barrel is 50ml and tha ratio C:B 2:1 ; C:B 10:1; C:B 25:1;(or it dipends on the sheeels.) Is the shape critical?And what presure can a 0,5L sprite bottle withstand?I may post a diagram.
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Unread postAuthor: boilingleadbath » Tue Feb 14, 2006 5:18 pm

Use the GGDT.
The shape is not terribly important.
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Unread postAuthor: pyromanic13 » Sun Oct 01, 2006 7:35 pm

could someone give me a link to GGDT? I always hear about it but have never seen it.

-thanks
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Unread postAuthor: pyromanic13 » Sun Oct 01, 2006 7:36 pm

rambo, whats you avatar?
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Unread postAuthor: rna_duelers » Mon Oct 02, 2006 8:04 am

Just type in GGDT in google you will find it.
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Unread postAuthor: POS » Tue Oct 03, 2006 11:40 am

can someone stick a number on that C:B ratio ? 2:1 ? more or less ?
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Unread postAuthor: CpTn_lAw » Tue Oct 03, 2006 1:36 pm

it's very logical, that the bigger the ratio is (for example a 10:1) the more powerful your canon will be. The reason is that, the under-pressure air reserve is still almost the same when you projectile is leaving the barrel...that means that if you pump your ai tank to 150 psi, you will have 150 psi pushing the projectile down the whole barrel, the pressure loss is unsignificant.
On lower ratios, let's say 0.5:1 the pressure loss is very significant, making that your projectile is pushed by less and less air while it goes down the barrel. so, you make your pneumatic according to this, and you other criterias, and you'll get just fine.
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Unread postAuthor: rna_duelers » Wed Oct 04, 2006 7:16 am

But there is a point were the larger ratio is to impacticle were by adding another 50cm of pipe will only make a gain of say 2m/s but i use a ratio of about 3:1 on my cannons works well.
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Unread postAuthor: brumby » Mon Oct 09, 2006 2:43 am

is there an online version of the GGDT or is there a mac version?
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Unread postAuthor: SquishY » Thu Oct 12, 2006 11:36 pm

What would be the most efficient and powerful ratio, or better yet make it a little easier for me and give the measurements. I have just over 5' of 4" pipe and almost 6' feet of 2" pipe, also when I get some 2.5" what lenght should it be for launching tennis balls and cola cans?
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Unread postAuthor: SquishY » Fri Oct 13, 2006 1:55 am

Will a 5:1 be good, to get this ratio my chamber(30") would be longer than my barrel(24") which IMO would look pretty silly. How ever the way it looks isn't the idea, would this sling densely wrapped wads of duct tape and w/e will fit down the barrel a good distance with considerable power?
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