cb ratio

[91sport_tn]

I have 2 feet of 3inch pvc for my chamber, and 2 feet of 2inch pvc for my barrel, about how much chamber should I cut off to make it fire efficiently?

[theBOOM]

Make your barrel longer.. Before I start explaining you your correct size... is your spudgun using metered fuel or is it a spray n spray?

[91sport_tn]

It is a spray and pray, and this is just an experimental gun. I already purchased all of the pvc, my options are cutting the chamber or leaving it as is.

[theBOOM]

Hm I would not suggest cutting the chamber maybe cutting it 4 inches or so, what I would suggest is getting a 6 or so feet barrel to get some good results.

[91sport_tn]

I may still get a longer barrel, but I also wanted a 4 inch chamber, but I could not find any 4 inch that was pressure rated.

[theBOOM]

Yeah a 4 inch chamber 2 feet long would require a 9.5 or so feet barrel .... a 3 inch chamber is still good just a little more compact, yet compact dosent mean less powerful.... ex. the gauntlet

[91sport_tn]

alright, thanks man, hopefully I will find what I need.

[SpudBlaster15]

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[D_Hall]

I won't ignore the pink elephant standing in the middle of the room....

...If you want it to fire *efficiently*, the first thing you'll want to do is meter your fuel and forget spray and pray.

[91sport_tn]

I am not going to dump an a** load of money into a cheap first pvc gun, I just want it to be a little quiter, and work a little better. So far it has only cost me $30, which makes me happy, but I am just experiment with it. I am already planning on going out to buy materials for my pneumatic.

[jackssmirkingrevenge]

I won't ignore the pink elephant standing in the middle of the room...

Was that a deliberate pun? The proverbial elephant in the room has no specific colour, unless one is inebraited

[psycix]

Don't cut it.
Spray and pray is hard to meter in smaller volumes.
On top of that, cutting the chamber would cut the power of the gun.
Even though efficiency increases, power drops even faster.

Unless a silent launcher is the goal, keep it this way.

[D_Hall]

I won't ignore the pink elephant standing in the middle of the room...

Was that a deliberate pun? The proverbial elephant in the room has no specific colour, unless one is inebraited

LOL... No, just an inadvertant usage. The "pink elephant" became a bit of an inside joke amongst some friends of mine many years ago. From there, it just rolled off my tongue...errr...finger tips without my realizing "where I was" when I said it.

[jimmy101]

I won't ignore the pink elephant standing in the middle of the room....

...If you want it to fire *efficiently*, the first thing you'll want to do is meter your fuel and forget spray and pray.

Well, actually, the first thing is you have to define what you mean by "efficient". Energy efficient? Operator efficient? Material efficient? Time efficient?

Any way...
A ~1 CB ratio would be a chamber half as long as the barrel. That's a bit small for the chamber so add 40% to get a CB near 1.5 and a chamber length of ~17". That sized chamber will get most of what is possible with 2 feet of barrel. A meter and a fan will make this an OK cannon. Muzzle velocity with half a spud of perhaps 200 feet/second.

[Boom_erang]

I would say about 12" should be right. That will give you good power but not too big of a bang... much bigger and I think you "waste" the power because so much of the combustion happens after the potato has left the barrel.