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Chamber Barrel ratio (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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Unread postAuthor: TwitchTheAussie » Thu Dec 13, 2007 8:00 am

Lets all do ourselves a favor here. Follow my way. 1:1xvalve speed. Voilah problem solved.
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Unread postAuthor: jimmy101 » Thu Dec 13, 2007 5:34 pm

Like JackS said, no real need to do extensive gun building to figure it out. GGDT will get the trend exactly right.

And, you need to decide what you are going for, maximum muzzle velocity or maximum efficiency.

The 0.2:1 CB gives about the maximum efficiency of a pneumatic gun.
CB's above 1:1 will give much higher muzzle velocities.

Compressed gas and chamber pipe is cheap so people usually go for performance and build guns with chambers larger than the barrel.
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Unread postAuthor: DYI » Thu Dec 13, 2007 5:43 pm

The 0.2:1 ratio is the most powerful as well as the most efficient, which makes loads of sense when you think about it. If you have a gun with a 0.2:1 ratio, and you cut off 4/5 of the barrel, performance will decrease dramatically. And if you're increasing chamber volume, an increased C:B will ALWAYS yield more energy, so there is no argument
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Unread postAuthor: daberno123 » Thu Dec 13, 2007 5:55 pm

I am doing the C:B ratio of pneumatics for my science fair project. I'm going to start off with a 10' barrel and then cut a piece off each shot and I'll see how the fps differs. I'll post the results once I have finished testing. (sometime in march)
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Unread postAuthor: DYI » Thu Dec 13, 2007 6:23 pm

I hope you do realise that you can do this entire project without ever building a cannon? All you have to do is model it on GGDT, for very accurate results. Doing hybrid C:B ratios would provide much needed information for the community, whereas doing pneumatic C:B ratios will provide us with information that we can already obtain simply by modeling the performance on GGDT.
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Unread postAuthor: JDP12 » Thu Dec 13, 2007 6:31 pm

yea go with GGDT, easy, simple, and saves a lot of time and trouble.

also, i forget who said it, but pneumatics are entirely dependent on valve design. I could have a perfect (if there is such a thing) C:B ratio on my pneumatic, but have a .5" PVC ball valve, which are nightmares to turn and restrict flow terribly, so that gun would suck.

or i could have a gun with a crappy C:B ratio, but an extremely good valve, (burst disk for example-fastest opening), and it would perform better than the gun with the good C:B ratio, but a crappy valve.

Decide what valve you want first essentially
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