SpudFiles

I had this idea today, the pic pretty much explains it but I'll describe it anyway. Basically it works off the concept that a perfect cb ratio will be very quiet. But a perfect cb ratio will only work at a certain pressure. Any higher and it will make noise, any less and the vaccuum behind the projectile will slow it down significantly.

My idea is to have a barrel that is quite a bit longer than the idea cb ratio, with one way valves set up before the projectile. When the projectile reaches the point where the pressure in the barrel is at atmospheric pressure (ideal quiet cb ratio), instead of creating a vaccuum behind it and losing speed, the one way valves will open and allow air in behind the projectile. Now the only losses will be the friction against the barrel, and this would be fairly small with a low friction ammo (like a snooker ball). With this barrel even if the pressure varys, it will still work without becoming too innefficient.
The diagram for this is for a pneumatic, but it could easily apply to a combustion.

Does anyone think this would work???

I think the idea of a longer barrel will work, as for your hop-ups i can only say try it, and good luck

Edit: if you can get the valves to work good it should be a good rig i think.

When the projectile reaches the point where the pressure in the barrel is at atmospheric pressure (ideal quiet cb ratio)

Let's assume you have a 1" pneumatic with a 1" x 24" chamber at 100 psi to give a decent amount of power, this gives us a chamber volume of around 19 cubic inches. This means that in order to achieve atmospheric pressure on muzzle exit, the total barrel+chamber volume should equal 1900 cubic inches, meaning the barrel has to be 2394 inches long

Hmm... I did the calculations twice but that's the figure I got.

It's a good idea but impractical unless you go for an extremely small chamber, in which case power would not be worthwhile.

2394, that's my lucky number

Aaah well, I never intended to actually build it but it was an interesting idea. It would be cool to see on a small scale though.

Dont forget the gasses cool down too and thus shrink in again.
It will be less then 2394 inch.

Neat idea. However a 200 foot long barrel is a bit extreme, even for FEAR which is like 50 if I remember right.

What about using the check valves in the opposite direction, further up the barrel, to release excess pressure before the projectile leaves the barrel?

Sort of like a muzzle break.... yeah, sort of. You get the idea. It would work like a muzzle break at really high pressures.

Granted I don't think it would be able to "silence" the gun but it should allow for a quiter firing.

Dont forget the gasses cool down too and thus shrink in again.
It will be less then 2394 inch.

That's true of a combustion but not a pneumatic.

Even with one of my mini pneumatics with a 0.79 cubic inch chamber starting at 300 psi, the barrel length needed is over 300 inches a 25 foot long "mini" Another solution would be to have holes in the barrel to send all that air into an exterior container of equivalent volume - hmmm, wait, that's what a silencer is

williamfeldmann wrote:What about using the check valves in the opposite direction, further up the barrel, to release excess pressure before the projectile leaves the barrel?

Sort of like a muzzle break.... yeah, sort of. You get the idea. It would work like a muzzle break at really high pressures.

Ummm, wouldn't that be the same as just holes in the end of the barrel?

-goose_man

Another idea: Make a HUGE chamber thats sucked vacuum and opened a split second after the main chamber is opened.
The projectile will get high pressure from the main chamber, then the vacuum chamber opens and sucks out (most of) the air.
Calculate this right and you will have zero pressure difference between the barrel and the outside air when the projectile leaves the barrel.

jackssmirkingrevenge wrote: Let's assume you have a 1" pneumatic with a 1" x 24" chamber at 100 psi to give a decent amount of power, this gives us a chamber volume of around 19 cubic inches. This means that in order to achieve atmospheric pressure on muzzle exit, the total barrel+chamber volume should equal 1900 cubic inches, meaning the barrel has to be 2394 inches long

Hmm... I did the calculations twice but that's the figure I got.

I think something is wrong. Using P1V1=P2V2 (must use absolute pressures) I get :
(19 * 114.7) / 14.7 = 148 cubic inches
Subtract the 19 cubic inches of the chamber since V2 is total volume
Which means the barrel needs to be 164 inches.

Still longer than practical, but not completely insane.

I think the check valves are a bit overkill. Having the barrel longer than needed wont significantly decrease performance unless it is a lot longer than necessary. Plus you could always just build it longer on purpose and cut it down slowly until you stop hearing a thwump from a vacuum forming when you shoot.

First, what causes the sound in pneumatics?
The Valve?
Barrel?

Like all problems, don't attack the result. Fix the source.

benstern wrote:First, what causes the sound in pneumatics?
The Valve?
Barrel?

Like all problems, don't attack the result. Fix the source.

The sound comes from the air escaping from the barrel. Same principal as a balloon popping. The source has already been attacked, in the form of a silencer. They simply slow down the air and let it expand into a separate chamber and it is then let out slowly. Once again a balloon analogy is used, if you pop a balloon it goes bang, if you slowly release the air it doesn't go bang.

EDIT: The problem is also the barrel, too short and the air is under more pressure, creating a louder report. The longer the barre, the less pressure the air is under as it escapes the barrel, creating a softer report.

The problem is also the valve, a better valve will make a louder noise because it dumps more air faster. But thats what you want....

Well then i would prefer a shrouded barrel. IE: a barrel witrh some holes in it inside a larger pipe. Then you don't need to increase barrel length and thus sacrifice performance.

benstern wrote:Well then i would prefer a shrouded barrel. IE: a barrel witrh some holes in it inside a larger pipe. Then you don't need to increase barrel length and thus sacrifice performance.

Increasing the barrel length won't sacrifice performance...cutting holes in the barrel would.