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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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Unread postAuthor: Gippeto » Mon Apr 21, 2008 8:13 pm

Actually, when hydro testing, air in the system is bad. Fluid pressure only.

The reason is that as mentioned, fluids do not store energy (compress) the way gases do. This means that in the event of a rupture, the pressure drops very quickly, and the energy (usually that stored by the gauge) is dissipated BEFORE it can cause harm. (like removing the flesh from your bones?)
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Unread postAuthor: DYI » Mon Apr 21, 2008 9:16 pm

_Fnord was spot on; liquid water is nearly incompressible, and cannot be compressed to any great extent with the kind of forces we're able to exert on it. Therefore, it doesn't store very much energy at all when it's pressurised compared to a gas.

Your design is just wasting power, since it is essentially the small volume of air doing the work. None of these things ever work quite as well under water, for obvious reasons, but more power is often the solution. If possible, use the compressed air charge to drive a piston which pushes the ammo forward. It could be a bit difficult to achieve without a lathe though.
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Re: Underwater gun

Unread postAuthor: psycix » Tue Apr 22, 2008 10:10 am

spudchucker wrote:I know that someone already thought of doing this but would this make it easyer to work? it would have water in the air chamber so that water would come out of the gun instead of air that would get rid of all the water to air physics right?


Back on the main thread guys...
I think that having water in the gun only reduces muzzle velocity since the water now also has to be pushed forward.
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Unread postAuthor: benstern » Tue Apr 22, 2008 10:56 am

I think this problem was discussed in an earlier thread. What we agreed upon was that saran wrap or aluminum foil in a union at the end of the barrel would mitigate the water in barrel problem. Even if it burst before the projectile reached it, the exiting air would not allow water to enter the barrel.
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Unread postAuthor: ROCK SOLID » Thu Apr 24, 2008 8:20 pm

you guys are wrong pressurising water can be presuurised look a this example , http://www.youtube.com/watch?v=a_QvUC3E ... edures.htm this guy has filled a pet bottle with water connected a hose to it and adding more water thus pressurising it :?
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Unread postAuthor: D_Hall » Thu Apr 24, 2008 8:40 pm

benstern wrote:Liquid water is an incompressible fluid. [...] It just can not be reduced in volume.

Not true. Not true at all. It just requires a LOT of force to compress it.


Extreme example: You think throwing a cup of water into a Neutron Star is going to increase the volume of said star 1 cup worth?



edit: And now I see I'm a few days late on this post... Why can't I delete it?
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Unread postAuthor: joestue » Thu Apr 24, 2008 8:52 pm

ROCK SOLID, I don't believe you understand what you said.

Air in the bottle, plastic stretches before it breaks, therefore increasing in volume... I have done the same thing, with 20 oz bottles, and 3 liter bottles.
when there is NO air in the system, the display is less than spectacular.

Back to the main topic, as psycix stated, the water has to be pushed forward, reducing velocity.

If you look at how a spear gun is built, the projectile is like an arrow, with regard to it's length:diameter. A bullet is not going to travel very far underwater.
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Unread postAuthor: benstern » Thu Apr 24, 2008 10:52 pm

D_Hall... I know it can be compressed, just not using stuff available to all most any of us and certainly not in the case of anything in the spudgun context.
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Unread postAuthor: D_Hall » Thu Apr 24, 2008 11:47 pm

joestue wrote:A bullet is not going to travel very far underwater.

Depends on the design. In the past 10 or so years there've been some very impressive designs that rely on super-cavitation. True, they don't go 1,000 yards or anything, but I've seen holes made through steel plates that were 30' under water (and the gun was on a helicopter).
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 25, 2008 12:51 am

D_Hall wrote:
joestue wrote:A bullet is not going to travel very far underwater.

Depends on the design


Agreed, depends on the design.
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Unread postAuthor: MrCrowley » Fri Apr 25, 2008 12:58 am

jackssmirkingrevenge wrote:
D_Hall wrote:
joestue wrote:A bullet is not going to travel very far underwater.

Depends on the design


Agreed, depends on the design.

The APS was developed as a combat diver weapon intended as a personal weapon for usage under water mainly against the enemy divers.

So if you're diving for crayfish, best bring along the APS incase you have some fierce comeptition with another diver? :D
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 25, 2008 1:04 am

The APS was developed as a combat diver weapon intended as a personal weapon for usage under water mainly against the enemy divers.


More like *innocent underwater whistle* Just bubblin' some air, attaching this mine to the enemy ship, tra la la la... (all in underwater Russian, of course) then all of a sudden, мой бог! Imperialist Yankee divers who might have some slight misgivings about having their vessel sunk!

What are you going to do, throw crayfish at them? Especially if they're wielding one of these :roll: :D
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Unread postAuthor: MrCrowley » Fri Apr 25, 2008 1:36 am

The P11
Super Secret Underwater Pistol
Cal 7.62 x 36


Super Secret?! :shock:

Gotta get me one of those :D
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 25, 2008 1:38 am

MrCrowley wrote:Super Secret?! :shock:


Image

Aye :D
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Unread postAuthor: MrCrowley » Fri Apr 25, 2008 1:48 am

What is known is that it will fire five shots, but after the five shots are fired, a significant delay in reloading, even slower than a revolutionary war muzzleloader. You must send the upper unit back to the factory for reloading!

Just hope there's six of you and one of them :wink:
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