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Reinventing the underwater gun

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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Reinventing the underwater gun

Unread postAuthor: PVC Arsenal 17 » Thu Feb 28, 2008 10:33 pm

I remember a thread by Atlantis a while back where he had the idea to place a valve at the muzzle of gun rather than before the projectile. The idea was you would open the valve and the air would move out of the barrel, carrying the projectile with it like a venturi effect.

I was thinking today about how I could fire some sort of wire dart (probably .40 dart) out of a gun underwater. Using a typical gun with an open muzzle would allow the barrel to fill with water. Upon firing, the dart would have to overcome water resistance. It would not gain enough velocity to do any damage.

I thought that by using a muzzle burt disc configuration I could allow the dart to gain velocity (in air) before encountering water resistance. When it does finally encounter water resistance, the plastic cone would separate from the wire due to drag and the wire would continue through the water at high velocity. I did some tests using my Fish Killer and I did find that when firing into water the cone would separate and the wire would continue on. It easily passed through 5 feet of water and penetrated through half an inch of concrete.

Any thoughts?
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Unread postAuthor: Carlman » Thu Feb 28, 2008 11:20 pm

or have you gun as normal and put a piece of cling film over the end of the barrel secured by a rubber band
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Unread postAuthor: ammosmoke » Fri Feb 29, 2008 12:16 am

But, if the projectile wasn't the perfect tight fit, which it never is, the film would be blown off by air escaping. Well, come to think of it, that air would also prevent water from coming in, so I think you are ok if you use that idea.
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Unread postAuthor: Hotwired » Fri Feb 29, 2008 7:49 am

Cling film should be fine for it but why would you want an underwater gun?

Not planning on harpooning goldfish are you?
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 29, 2008 8:06 am

Why not just built an ordinary pneumatic and seal the barrel? with a muzzle mounted valve, the air trying to accelerate the projectile would also have the fight pressurised air ahead of the projectile, you're better off having it accelerate through air at atmospheric pressure.
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Unread postAuthor: Jared Haehnel » Fri Feb 29, 2008 8:51 am

fight pressurized air ahead of the projectile


Agreed... however you would also consider if go below a couple feet of water the pressure from the water will prematurely burst your burst disk...
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 29, 2008 9:00 am

Jared Haehnel wrote:If you go below a couple feet of water the pressure from the water will prematurely burst your burst disk...


... so you should make it a bit stronger ;) the air flowing by the projectile will likely burst it before the projectile reaches the disk.
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Unread postAuthor: Jared Haehnel » Fri Feb 29, 2008 9:09 am

I kind of like the ball valve a the front of the barrel idea... I'll have to read the previous thread but it seems like it should work with reasonably light objects...

How deep do you plan on using it?
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Unread postAuthor: homedepotpro » Fri Feb 29, 2008 9:55 am

i used sandwich bag material as a burst disk in my submersible gun.

http://www.spudfiles.com/forums/submersable-speargun-t9586.html

one thing to consider is every 9 feet is another atmosphere worth of pressure. so the deeper you go the more power you loose.
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Unread postAuthor: Fnord » Fri Feb 29, 2008 11:34 am

Keep in mind being under water while firing a gun may not be great for your hearing.
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Unread postAuthor: Jared Haehnel » Fri Feb 29, 2008 11:54 am

Keep in mind being under water while firing a gun may not be great for your hearing


:lol: thanks for thinking of the stuff we never do
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Unread postAuthor: Fnord » Fri Feb 29, 2008 12:26 pm

I was referring to homedepotpro's post, which implied actually being underwater while firing.
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Unread postAuthor: Jared Haehnel » Fri Feb 29, 2008 1:04 pm

What other purpose would there to be biulding an under water spud gun? Its not much fun unless you could shoot at something underwater and it would be hard to aim at anything unless you your self were under water.

You did bring up a good point with it being loud though I don't think any one of use would have thought of that...
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Unread postAuthor: PVC Arsenal 17 » Fri Feb 29, 2008 3:41 pm

I suppose simply sealing the barrel off would make more sense. I just thought that a muzzle valve would kill two birds with one stone because it also seals off the barrel.
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Unread postAuthor: Jared Haehnel » Fri Feb 29, 2008 3:51 pm

Makes alot of sense to me and You can biuld it in a way that if it doesn't work you can continue to play with it and at least have a decent spud gun....
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