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Shooting fish

A place to ask general spud cannon related questions.
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Shooting fish

Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 6:58 am

The titel is not what it implies. I do not plan to shoot fish but the following problem has been goign through my mind for the last few days:

When you shoot at water your projectile first slows down once hitting the water, it keeps going , soemtimes in an arch, for another 20 or so cm before stoping and, in case of a round lead ball, sinking vertically to the bottom. I was wondering how you could get your projectile to keep a strait "flight" path in the water. Spear guns manage to so I was wondering if perhaps the projectil needs top be accelerated under water. This proved to be wrong as there was barely any differenc ein what happened. Next i thoght that perhaps acceleratign the projectile with a gas was the probalem as the gas would stop accelerating the projectile as soon as it reached the water So maybe the answer to my question is to acclerate the projectile with water, in any case I would like to know how would I get my projectile to remain on a strait flight path under water, maybe soem of you can help me out here.

P.S. I am sorry if this post is confusing, ask If somehtign is not clear.
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Unread postAuthor: littlebro05 » Sun Mar 08, 2009 8:39 am

Time to get the mythbusters! is all I can say...

I think the spears are carefully engineered to be hydrodynamic... so I would try to make that leadball into like an arrow or something. I dunno just suggesting
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 8:52 am

Well, i some how think i have to use water and launch my projectile under water, like that a continous wave of water is behind the ammo pushing it forward and th ammo doesnt have to break through the water but starts under water already...
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Unread postAuthor: Sticky_Tape » Sun Mar 08, 2009 8:58 am

The spears travels underwater because they are very skinny. I think what makes them fly underwater is that they don't need to move the water so much to travel, rather they cut through it. What are you more likey to pass through your hand? A hammer or a needle? The needle because it has a very small cross sectional surface area and it doesn't need to move your flesh so much rather it cuts through it :D hope you liked that little exsplaination.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: FishBoy » Sun Mar 08, 2009 8:59 am

well, i know arrows are effective when shot into water, and i think the difference is that when the tip of the arrow hits, the mass of the shaft behind it prevents it from slowing down like a bullet. Also, arrowss generally have narrower points/tips.

Basically, try some kind of low-profile dart/arrow ammo and see if that works.
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 9:22 am

Hmm so I would need to make some kind of lead dart or very long bullet right? the tip would also need to be sharp and the diameter would need to be as small as possible. Would length play a role?
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Unread postAuthor: Sticky_Tape » Sun Mar 08, 2009 9:54 am

Not as much a wieght piontyness and diameter I don't see the problems with the dart being and shorter than a foot. I actually did a test in my bathtub with my 5mm pistol a very pointy dart. The target was a pop bottle filled with water the gun was 3' away and the barrel had a layer of tinfoil over it and the gun was charged to 300psi. I fired the gun the dart traveled through the water and through one side of the pop bottle taking the tail of the dart off and sticking the matel shaft of the dart into the other side. The dart was heavy for it's size, very pointy stable and olny about 1'' long. Pretty good eh?
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 10:02 am

So length doesnt really matter, but how wold I make a dart stable? I cannot attach fins as a do not with to use wadding or a sabot, so...
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Unread postAuthor: Sticky_Tape » Sun Mar 08, 2009 10:18 am

Weight the front of the dart. Basicly you need the cog ahead of the coa.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: maverik94 » Sun Mar 08, 2009 10:22 am

speakin of mythbusters, there is an episode called "bulletproof water" and they shoot at an underground target with different guns. They find that the slower firing guns, such as the shotgun and the pistol were much more effective underwater. However, I think something like a bow or a blowgun would be more effective underwater than a bullet. Also, you need to be sure that your round has little buoyancy sothat it doesnt just float up to the surface.
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 10:26 am

I know that episode, but a spud gun has very different velocities that a fire arm, no need to compare. I would use lead so boyancy is no problem. What about a pellet would that work under water? How about ou guys coem into the chat, easyer to discuss thigns there.
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Unread postAuthor: D_Hall » Sun Mar 08, 2009 10:43 am

Guns work pretty well if you have the right bullet.

Google for "supercavitation."
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 11:01 am

hmm, how exactly could I replicate this for a spud gun? What would I make the mold from and how coudl I make the shape? Thanks for the idea D
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Unread postAuthor: Ragnarok » Sun Mar 08, 2009 11:07 am

My advice would be to replicate what the APS underwater assault rifle did, essentially firing steel rods - high sectional density to help them overcome drag, and hard enough that they didn't break apart or deform like lead bullets would. The effective range was still only about 100 feet at maximum - however, considering that most rounds not intended for use underwater break up or are slowed to non-fatal speeds well within a tenth of that, it's a big difference.

Basically - get some steel rod in about 6mm size, make it into "darts", make some sabots... much better than trying to mess around with lead.
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Unread postAuthor: john bunsenburner » Sun Mar 08, 2009 11:16 am

Could i forget bout the sabbots, and use 5mm rods that fit into the barrel i have? Would i have to fire underwater or can i be above the water when fireing, anythign else I need to know?
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