SpudFiles

I just came up with these plans for my 1st pneumatic cannon. I dont know if its a good idea because it might be too heavy, and that the chamber(4'')is much bigger than the barrel(1 1/2'').Will thes work good?



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well, it should work, you would get better performance if you made the barrel longer
or if you wanted the barrel that short, you could shorten the chamber alot

how much longer?

well, you could probably go almost double the length of what you have posted

k, thanks

Also I think it's better to place the valve at the very beginning of your barrel.Not at the end of your reservoir.Think about it.THe way you've drawn it the air can expand after it "leaves" the valve through the bend before it hits the projectile.Loss in performace if you ask me.

Brian the brain wrote:Also I think it's better to place the valve at the very beginning of your barrel.Not at the end of your reservoir.Think about it.THe way you've drawn it the air can expand after it "leaves" the valve through the bend before it hits the projectile.Loss in performace if you ask me.

Absolutely correct. Dead space minimizes performance.

also put the schrader valve on the side where 2 pieces of PVC overlap. the reducer you drew is the "bell" type which is not pressure rated, use a coupler and some pressure rated reducer bushings

Eh, dead space reduces preformance, but is the loss of preformance by the barrel space the sprinkler takes up more noticeable?
This sounds like a job for the GGDT! <insert searchlight-projected picture on cloud here>

Both guns being modeled Use a 50g projectile in a 1.59" bore, with the sprinkler valve data provided by the GGDT site.
The valve-on-bottom design assumes deadspace is 26 cubic inches, and uses a barrel length of 49". Muzzle velocity at 100 PSI is 354 fps, at 50 psi it's 278 fps.
The valve-on-top design assumes deadspace is 3 cubic inches, and subtracts 5 inches from the barrel length (uses 44" barrel) to account for the length of the valve. Muzzle velocity at 100 PSI is 329 fps, at 50 psi it's 255 fps.

...so yeah, putting the valve on the bottom is your best bet. That being said, you could use a 24" chamber (lighter, easier to fill) and only lose about 3 feet/sec.

thanks, that helps . I just found only have 30'' of 4'' pipe left, so I couldnt make the chamber as big as I planned. And 24'' would make it lighter too. ............I still need to know if the reducer that I have is ok to use on this cannon.

Its probably fine as long as you don't take it very high. DWV fittings are not rated for pressure. Do as another poster suggested, use pressure rated bushings and couplers.