SpudFiles

Lets all do ourselves a favor here. Follow my way. 1:1xvalve speed. Voilah problem solved.

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.

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

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)

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.

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