SpudFiles

I feel like your tennis ball is creating a Vacuum about 3/4 down the barrel. That POW is probably the instantaneous release of a vacuum. Think Champagne bottle. If you were to cut the barrel down somewhat, I think this would go away.

Model it in GGDT and check out the different plots. You will find that it will give you a "barrel too long" error.

Double diameter is enough for a silencer, just run it "coaxial" over the whole barrel.
Note, you can shorten the launcher as you can run it at a higher pressure without getting noisy.

Well seeing as my cannon is already only 8" long, there is not much shortening to do... In fact I would probably have to lengthen it to 12" in order to add enough of a length with holes in. Still, I have been considering it, just because it will help which ever way you are off. If you have too much pressure, a vacuum, either way it will act as a buffer of sorts.
Probably the best thing to make it out of would be the 2-3 liter soda bottles, because they are so light, and you can use their tapered necks as baffles.

Lentamentalisk wrote:to emphasize ALIHISGREAT's point, when you look at a silencer for a gun, airsoft, or paintball, you will notice that the diameter of the silencer is several times that of the barrel. On the order of 4-6 times the diameter. That means to get a similar effect, the silencer for the TB cannon would have to be at minimum 1' diameter! Good luck even finding pipe that size, not to mention carrying it with out the help of 3 others...

If they could, they would make them in the order of 2,000-10,000 times the barrel diameter - with silencers, bigger is better, simple as that. The limits are decided by what is practical to carry in terms of weight and balance, not performance. Firearms operate at pressures far greater than spudguns so any comparison isn't really valid. Also, they not only provide expansion volume but rob heat from the propellant gasses which further reduces their pressure, an effect which pneumatics cannot benefit from.

Valid point. In fact, it is possible for a silencer to increase the volume of a pneumatic, (though not very likely) due to the fact that the gases will often be coming out at -80f if not lower...

Still, depending on your size constraints, if you would be willing to make it a lot fatter in order to decrease the length, then a silencer is a good way to go.

Lentamentalisk wrote:Still, depending on your size constraints, if you would be willing to make it a lot fatter in order to decrease the length, then a silencer is a good way to go.

You can also be a bit innovative in that just because most suppressors are tubes around/at the end of the barrel, that's not the only way to go.

Look at the "brick" suppressor on the early HK SOCOM prototypes:



That's got at least double the volume of a conventional suppressor of the same length. Also, say you have a hollow stock or grip, you could easily connect these to the suppressor for extra volume without adding bulk.

jackssmirkingrevenge wrote:

Lentamentalisk wrote:Still, depending on your size constraints, if you would be willing to make it a lot fatter in order to decrease the length, then a silencer is a good way to go.

You can also be a bit innovative in that just because most suppressors are tubes around/at the end of the barrel, that's not the only way to go.

Look at the "brick" suppressor on the early HK SOCOM prototypes:

That's got at least double the volume of a conventional suppressor of the same length. Also, say you have a hollow stock or grip, you could easily connect these to the suppressor for extra volume without adding bulk.

Thanks for all the great ideas guys. I'll be a project for another day. The ham get together is late July. I'm thinking I need to work on the contest entry in the mean time. So much to try, so little time.

Lentamentalisk wrote:I am just wondering how much noise the ball makes just by rushing down the barrel really quickly. How much of a sound wave is created by forcing all of that air out... Would that be a significant amount?

In that case, a far better option for you would be to switch to a high pressure, low volume chamber, and a much shorter barrel, so that you don't move as much air.

Sweet success at last. The short barrel remained noisy. The long barrel has a sweet spot at just over 100 PSI. I noticed it when trying the 7 foot TB barrel from the t shirt launcher on the marshmallow cannon. In the video the only noise heard is the valve in the tank. The TB launch itself is practically silent. Take a listen.

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110 PSI shot, ~7 second hang time. silent.. Nice. Just need to add the fishing reel and I'm ready for the park. Follow the link to view the video full screen to watch the landing bounce a few times. It's hard to see, but the first bounce appears to be about as high as the tree behind it.

Very odd... So the pressures that weren't enough to get it out of the barrel were loud, but once it leaves, with enough pressure, its near silent...
It would be interesting to model it in GGDT and see what it says about your barrel pressure, in each case.
Good job, I really hope I can get mine half that quiet.

See, it's possible to be silent without a silencer

Lentamentalisk wrote:Very odd... So the pressures that weren't enough to get it out of the barrel were loud, but once it leaves, with enough pressure, its near silent...
It would be interesting to model it in GGDT and see what it says about your barrel pressure, in each case.
Good job, I really hope I can get mine half that quiet.

And

See, it's possible to be silent without a silencer Wink

Great graphic Jack. Mind if I borrow it to paint on my antenna launcher barrel?

I did find it strange that when we expected a vacuum pop, it was silent. I thought about it for a while and wondered if we were missing something.. like maybe the mass of the moving air. It's in motion. It may be possible when calculating the expansion for 0 psi on exit, we overlooked the mass of air following the ball. I'll need to get a higher pressure pump and test at the 0 psi exit gas expansion prediction. We may actually have a positive pressure wave at the ball while the tank area is negative. Needs further investigation.

Lentamentalisk, If you can get a short barrel quiet, let me know! I wish you luck. I may have jumped over the sweet spot and figured it wasn't quiet enough. Again, more testing required. GGDT needs an update to predict the silent launch volume.

Slight necro, but its important to point out that in legal terms "firearm silencers" is an extremely broad term that applies to anything that could be used to silence a firearm, including even something that is built into a spud gun. Be careful if ya do go working with silencers as if I remember right it is a felony just to own one. It was something crazy like "anything that could reduce the noise generated by a firearm by as little a 1 decibel, even if it destroys said silencer in the process." Kind of absurd if you ask me, a towel covering the barrel would do this; but that's the law...at least in the states. You can do it legally, but it takes some ATF hoops and about 200$ I believe.

Just be careful and check the laws.

Just1ChanceFree wrote:You can do it legally, but it takes some ATF hoops and about 200$ I believe.

Just be careful and check the laws.

I think the best reading for stateside tinkerers as far as suppressor legality is concerned is this article from the Beeman site.

Technician1002 wrote:Great graphic Jack. Mind if I borrow it to paint on my antenna launcher barrel?

Bit of a late reply but not my graphic, nicked it off the excellent Finnish gunwriters site

This is an old thread, but has anyone figured out how this phenomenon of becoming silent works? Any ideas/thoughts/conclusions since this was initially posted? This is very interesting stuff.

Well, you basically use the barrel as the silencer. If the volume of the barrel is great enough, the pressure in the barrel when the projectile exits is atmospheric. If the barrel is too long, you get a vacuum and a pop.

This has been explained in the thread, possibly even in the first post. The most likely reason it didn't work at first is because Tech screwed up his math or something