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Supressor Question

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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Supressor Question

Unread postAuthor: grock » Tue Jun 22, 2010 11:03 am

I was thinking of making a suppressor for my GB gun. In a perfect world, i would be nice for it to be completely silent. my thinking on suppressor volume is that it has to equal the expanded volume of my chamber.

for example (to keep the math nice), if i filled my chamber to 150psi (~10x atmospheric pressure) wouldn't my suppressor need to be ~10x my chamber volume?

also, do i count my barrel as part of my "expanded" volume?
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Re: Supressor Question

Unread postAuthor: SpudFarm » Tue Jun 22, 2010 11:09 am

grock wrote:I was thinking of making a suppressor for my GB gun. In a perfect world, i would be nice for it to be completely silent. my thinking on suppressor volume is that it has to equal the expanded volume of my chamber.

for example (to keep the math nice), if i filled my chamber to 150psi (~10x atmospheric pressure) wouldn't my suppressor need to be ~10x my chamber volume?

also, do i count my barrel as part of my "expanded" volume?



You will have to think of the noise of the projectile going down the barrel to. Atleast my cannons all make bad noises while the projectile is traveling down the barrel.

But your statement makes sence. The barrel would not count since it's not under pressure.
Someone will probably come and write something smart that makes me feel stupid in a moment :P
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Re: Supressor Question

Unread postAuthor: jackssmirkingrevenge » Tue Jun 22, 2010 11:15 am

grock wrote:My thinking on suppressor volume is that it has to equal the expanded volume of my chamber


It should be at least that, but in reality, the simple rule of thumb is make it as big as you are comfortable with.

Pneumatics are remarkably hard to suppress, I've heard suppressed rimfire rifles much quieter than similarly suppressed air rifles of lower power. The advantage of firearms is that the expansion of the propelling gasses is down to heating, so cooling those gasses plays as much of a role in sound suppression as allowing them to expand in a contained space.
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Unread postAuthor: Technician1002 » Tue Jun 22, 2010 12:44 pm

To understand sound. Sound is a pressure wave.

High frequency sound is very audiable. Subsonic frequencies are more felt than heard. The goal of a suppressor is to prevent a sudden (high frequency) pressure wave so the sound is mostly subsonic.

The sudden pressure front is filtered to remove the sharp rise and widen it to remove the crack and change it to a thump. You won't get silent, you simply change to subsonic.

The bigger the burst of air, the bigger the filter chamber to spread out the time of the burst of air released.
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Re: Supressor Question

Unread postAuthor: SpudBlaster15 » Tue Jun 22, 2010 1:09 pm

grock wrote:also, do i count my barrel as part of my "expanded" volume?


Yes.

In a simple world, you would want the (barrel volume + suppressor volume) to be equal to or greater than the expanded volume of the chamber. However, there are other factors that make Boyle's Law only a rough estimate. In reality, go with JSR's suggestion: Make the suppressor as large as you are comfortable with.
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Unread postAuthor: Technician1002 » Tue Jun 22, 2010 5:25 pm

Here is an example showing a barrel used as a suppressor. A very large volume barrel is attached to a very low volume chamber. At relatively high pressure the combination becomes almost silent launching tennis balls. Pressure is high enough the pop from uncorking the barrel under a vacuum goes away and low enough there is no pop from uncorking under pressure. There is no suppressor other than barrel length. The clank of the piston snapping open in the steel tank is the loudest part of this launch.

This combination is loud.
Image

This combination becomes silent at about 110 PSI
Image

Hear it here.
http://www.youtube.com/watch?v=ZUTXomfdLTE
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Unread postAuthor: grock » Wed Jun 23, 2010 5:06 pm

awesome. thanks guys
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 24, 2010 1:30 am

Technician1002 wrote:Here is an example showing a barrel used as a suppressor. A very large volume barrel is attached to a very low volume chamber. At relatively high pressure the combination becomes almost silent launching tennis balls.


Not just pneumatics...

Extra barrel length = a suppressor

Extra ten inches or one full foot of barrel and bore length is able to act as a suppressor. Volume of the extended bore shall lessen the pressure of powder gasses emerging muzzle. Friction between rifled bore and the bullet slows down muzzle velocity; Q.E.D...

When using Standard Velocity .22 LR ammo, the bullet velocity is increasing to ca. 400 mm (16") distance from the chamber, but after passing this culmination point, is the velocity decreasing, because bore friction shall overcome the thrust of powder gasses, pushing the bullet towards gun muzzle.

Bore pressure is decreasing, because volume of the bore behind the bullet is expanding and temperature of gasses is declining. Barrel metal absorbs the heat, and rapid decrease of the bore pressure cools also powder gasses down. "Diesel Effect" can be reversed too..!


Works for shotguns too :)
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Unread postAuthor: kozak6 » Tue Jun 29, 2010 3:31 pm

The Frankford Arsenal silencer book assumes the volume of a typical firearm suppressor being 20 times that of the barrel in a calculation chapter.

A significant part of silencing is slowing down the release of gas, accomplished in one way through simple expansion.

I'm curious what could be achieved through using x-slit wipes.

I still find the legality aspects very troublesome, though, so I think the long barrel type above is probably one of the better ways to go.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 29, 2010 4:26 pm

kozak6 wrote:I still find the legality aspects very troublesome, though, so I think the long barrel type above is probably one of the better ways to go.


You could always make it as permanent as possible, in which manner it could not be removed and attached to a firearm with conceivable ease.
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Unread postAuthor: grock » Tue Jun 29, 2010 8:33 pm

hang on... so a supressed firearm with a permantly attached supressor is legal?
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 30, 2010 5:45 pm

grock wrote:hang on... so a supressed firearm with a permantly attached supressor is legal?


Only with the appropriate license.

Have a read through this, very useful for those stateside.

According to the highly capable firearms lawyers who have advised me on this matter, the courts could well frown on any device that is CAPABLE of being attached to a firearm which could reduce the discharge sound by even that one decibel for even one shot – after all that could be the shot that kills a president.

Some airgunners have felt that if their moderator is securely attached to an airgun, or best of all, built into it as part of the airgun, then it would be exempt from these draconian laws. It does not make any difference if the airgun sound moderator is permanently attached or even built in as part of the airgun! There is NOTHING in the law as to what, or how, the device is attached - to discuss that point is just dreaming or at best just an opinion from some officer- with no impact in court!! The talking heads tell each other this excuse over and over. Even the law authorities have noted that a moderator on an airgun, even one built into the airgun, can indeed be removed, perhaps by even machining away the airgun, or unscrewing the permanent-looking barrel shroud unit,, and then adapted for use on a firearm- i.e. it is capable of moderating the discharge of a firearm - for at least that one decibel reduction for one shot rule. In the law against brass knuckles, there is no mention of allowing their possession if they are permanently embedded in a plastic display block or welded to a metal display plate; it merely says that that possession of brass knuckles is illegal.


I guess it would better your chances but if they were really out to prosecute you it would appear that you wouldn't be completely in the clear.
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Unread postAuthor: Ragnarok » Wed Jun 30, 2010 6:06 pm

Even the law authorities have noted that a moderator on an airgun, even one built into the airgun, can indeed be removed, perhaps by even machining away the airgun

Well, that sounds a very efficient way of going about it... as opposed to just using that machining capacity to make a new suppressor.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 30, 2010 6:18 pm

Ragnarok wrote:Well, that sounds a very efficient way of going about it... as opposed to just using that machining capacity to make a new suppressor.


That's the irony here, anyone with the facilities to make such a move would me capable of building a much more efficient suppressor from scratch, ah well...
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