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Pneumatic Silencer?

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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Unread postAuthor: Northir » Thu Sep 17, 2009 3:19 pm

while this is true it was my first cannon off of plans from MrCrowley, i didnt know how loud it would be when i was building it, but i do enjoy the report, my land lord just doesnt
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Unread postAuthor: Technician1002 » Thu Sep 17, 2009 4:44 pm

Northir wrote:while this is true it was my first cannon off of plans from MrCrowley, i didnt know how loud it would be when i was building it, but i do enjoy the report, my land lord just doesnt


Proper high speed valves do tend to go off with a bang. They are quieter at much lower pressure. Try it when at home on 10-25 PSI and see if it appears more sane to your landlord. It will still pack a punch. On my large cannon very low pressures are still fun and not nearly as noisy.

At 100 PSI it is downright intimidating with a shorter barrel.
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Unread postAuthor: covey12 » Thu Sep 17, 2009 5:43 pm

well here we go again, im not gonna rag on you about it but there must be atleast 50 topics on this, not sure if its legal, so on that note i will call this a muffler lol it won't silence it completley anyways,

THIS MIGHT DECREASE(not by much i hope) YOUR PERFORMANCE AND DEFINITIVELY MAKE IT TOP HEAVY

guessing that you have a 1.5inch barrel, get some bigger diameter pipe ( half the length of your barrel atleast 1.5in bigger than the barrel diameter) two reducers that fit from the barrel to bigger pipe (dwv will work on this because it won't be under very much pressure) drill, and some bits ( i would use 1/4-1/2 in.)

first, drill a lot of holes through out the front half of your barrel that the muffler will cover, on all sides of the pipe

second, sand out some of the smaller diameter of bot reducers so your barrel slides smoothly through them, once it does, glue each of them on to each side of the larger pipe.

third, slide your barrel into the muffler, make sure it covers all of the holes you drilled, and glue it into place

4, make sure your barrel's bore is still smooth, put some sandpaper on a dowel rod and sand out any rough spots near the wholes as necessary

this should work theoretically because some of the gasses escaping the barrel will go into the bigger chamber and that way when the ammo leaves the barrel the gasses comeout in a more "controlled" manner you could say
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Unread postAuthor: Northir » Thu Sep 17, 2009 6:02 pm

thats almost exactly what i had in mind, i think ill make it detachable, thinking a drilled out piece of barrel slipped into a piece of 3" PVC and a coupler on one end to attach to the barrel
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Unread postAuthor: D_Hall » Thu Sep 17, 2009 6:06 pm

jackssmirkingrevenge wrote:A smaller chamber and longer barrel will cut down significantly on noise. Given the size of your launcher, the volume of silencer needed to adequately reduce noise levels would result in the cannon being somewhat clumsy. Still, a reasonably sized can on the muzzle end will take the edge off the muzzle report and make the noise more "socially acceptable" so to speak.


More or less what I was going to say.

I used to have a 450 fps golf ball gun that wasn't any louder than a conversation. Really, it was *quiet*. Only reason? Long barrel.
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Unread postAuthor: Northir » Thu Sep 17, 2009 6:28 pm

this is what im thinking, so it can be removed as needed its about 35" in length
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Image

maybe with insulation inside or something else to absorb the sound
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 17, 2009 8:03 pm

I would still consider cutting down a little on chamber volume as well as making a suppressor/

Northir wrote:maybe with insulation inside or something else to absorb the sound


Image

(Ignore the dimensions, this was from another design)

The inner tube should be heavily ported, and you could have wooden disks (or be original, cut down soda bottles/ drilled out soup tins, there are countless improvised possibilities, I even used lego blocks :D) spaced out as baffles to make it multi-chambered and more effective.
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Unread postAuthor: Northir » Thu Sep 17, 2009 9:25 pm

thats pretty close to what i was thinking, should i have holes in the outer section?
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Unread postAuthor: inonickname » Thu Sep 17, 2009 11:35 pm

No. Holes in the outer shroud is just an unnecessary (and possibly negative) complication.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 18, 2009 12:45 am

Northir wrote:thats pretty close to what i was thinking, should i have holes in the outer section?


No no no a thousand times NO!

I would really like to know where people get this idea! There isn't a single effective suppressor of any kind out there with holes in it other than the point of bullet entry and bullet exit.

In something like the Knights ICS, what appear to be holes in the can are in fact holes through an out jacket to promote cooling when firing at a rapid rate - the inner tube remains sealed.
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Unread postAuthor: Northir » Fri Sep 18, 2009 1:06 am

i was thinking "Where does the air go" thats where i got the idea anyways, i have my inner barrel half drilled out just need to find my 1/8 bit, i spaced them about a 1~1 1/2" apart then staggered, now that i look at it it kinda looks spiraled around, not sure if thats a good or bad thing
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 18, 2009 1:15 am

Northir wrote:i was thinking "Where does the air go" thats where i got the idea


The point of a suppressor is that the air expands in a confined place, losing pressure in the process, before it exits to the atmosphere. With holes in the outer tube, it's going straight to the atmosphere so the suppressing effect is lost.

anyways, i have my inner barrel half drilled out just need to find my 1/8 bit, i spaced them about a 1~1 1/2" apart then staggered


This sounds like far too little porting, for your calibre I'd be looking at at least 0.5" porting 1.5" apart centre to centre.

now that i look at it it kinda looks spiraled around, not sure if thats a good or bad thing


This is usually done with ported rifled barrels where the holes are drilled within the rifling grooves as in the Russian VSS short range sniper rifle:

Image

Supposedly the spiral pattern helps with suppression but there is no hard physical data to back this claim, the main reason it's done is to follow the rifling and maintain the integrity of the barrel's inner surface.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 18, 2009 1:42 am

D_Hall wrote:I used to have a 450 fps golf ball gun that wasn't any louder than a conversation. Really, it was *quiet*. Only reason? Long barrel.


Works for powder burners too:

Silence without silencer

Sometimes the muzzle-blast is a "whisper" even without presence of suppressor device. .22 rimfire rifle with an extra-long barrel (length more than 600 mm / 23 ½") can be very quiet, when loaded with CB Short or Long cartridge, also known as ZIMMER-load or simply Z-cartridge. German word "Zimmer" means "room" or "indoor". Z-loads are intended for gallery practice, but they are useful for pest control or even for small-game hunting. Light bullet, with muzzle velocity not very much more than 200 meters per second, is more lethal than most of peoples dares to believe - or even to dream !

Original Z-loads hadn't powder charge at all, but just a priming pellet slightly more powerful than needed for normal rimfire cartridges. Frenchmen FLOBERT and HOULLIER developed the first versions of them, BB-caps, CB-caps and Bosquettes, during the first half of 19th century. Usual .22 Short or Long Rifle standard velocity cartridge, with a nominal muzzle velocity ca. 340 to 360 meters per second, may be quiet when shot from some rare .22 rifle with a VERY long barrel.

A quiet old "Long Tom"

Finnish Army used some decades ago .22 rimfire rifles, exclusively chambered either for LR or Short cartridges, with barrel length almost amazing, 825 millimeters (32 ½ inches!) When loaded with standard velocity.22 LR Vostok cartridges or Lapua Championships (nominal muzzle velocity ca. 340 m/s), the muzzle blast was as noisy as that of SHERIDAN's compressed-air rifle, pressurized with five or six pump piston strokes. Bullet's flight noise was always absent.

Reduced pressure AND velocity

When loaded with .22 Short cartridge, made for Olympic Pistol shooting (= Rapid Fire Match), the hit of "Long Tom's" heavy striker was a dominant sound. Then came snap of bullet from direction of the target. It was also possible too see, even without magnifying optical sight, the slowly flying bullet. Nominal bullet's muzzle velocity of these .22 Short Pistol Match cartridges was 310 m/s, shot from 4" test barrel.

Author hadn't yet the chronograph in late 70s, when he became acquainted with that rare variation of Mosin-Nagant model 1891, but velocity of bullet might be approximately equal with that of similar .22 Winchester Long-Z bullet, shot from usual rifle barrel; length 20 to 22 inches.

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..!
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Unread postAuthor: Northir » Fri Sep 18, 2009 2:48 am

well doubled the amount of porting, will have to wait till tomorrow to get the fittings ill need, just need to figure out how to sand the inside of the barrel
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Unread postAuthor: Technician1002 » Fri Sep 18, 2009 11:04 am

Northir wrote:well doubled the amount of porting, will have to wait till tomorrow to get the fittings ill need, just need to figure out how to sand the inside of the barrel


I use split dowel on a rod with stick on sand paper. It works nice.
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Galvanized iron pipe nipple polished with sandpaper on a dowel.
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