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Water-Jet Pistol

Not a toy!
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See link for info on water jets.
Note that a water jet can cut through several inches (more than twice that many centimeters) of metal. Obviously if parts of your body were in the way of such a jet, you would regret it.

Well, anything can be used as a weapon, so...(warning! this is not a nice Idea!)
Consider a cartridge not unlike an air-rifle CO2 cartridge, but MUCH stronger, and filled with extremely pressurized water. You place it in the pistol, and when you pull the trigger, a valve is snapped open that lets the water out though an extremely narrow barrel. This is ONLY a point-blank-range (execution) weapon, so you have to have the nozzle of the pistol right next to the victim -- at the head, say. The water jet makes its cut, and death follows quickly.

The murder investigators are puzzled. There is an exceptionally small entry hole in the skull, but no exit hole, no bullet -- and no stiff wire is strong enough to penetrate the skull! If the murder had been done on a hot dry day, most of the water would have dried up, leaving a mystery...until this type of weapon becomes widely known, that is.

Vernon, Aug 16 2005

Industrial Water Jets http://science.hows...com/question553.htm
As mentioned in the main text. [Vernon, Aug 16 2005]

Ice II, Ice III, etc. http://www.lsbu.ac.uk/water/phase.html
As mentioned in an annotation [Vernon, Aug 16 2005]

Oceanic Trench and water pressure http://en.wikipedia...iki/Marianas_Trench
Compare to pressure used in a water jet. [Vernon, Aug 16 2005]

incompressibility http://www.fas.harv...ibilityofWater.html
Harvard doesn't see all the implications... [GutPunchLullabies, Aug 17 2005]

[link]






       how much water would that pistol have to contain in the bullet dept thingy? bit weighty wouldn't you say?   

       ah sorry didn't read it properly.   

       pressurised water? could you run a car with that technology?
po, Aug 16 2005
  

       [po], the blast of water in this Idea is very short-term. And pressure tanks of any sort in vehicles are frowned-upon, due to accidents happening (tank ruptures are more deadly than the accident).
Vernon, Aug 16 2005
  

       Oh lord, [Vernon] has joined in the weapons craze.
When I was reading the title I was wondering how obfuscated he could make a simple water-pistol.
I fail to see why there would be no exit wound though.
hidden truths, Aug 16 2005
  

       [hidden truths], I'm pretty sure that when cutting into the skull and going through the brain, the force of the jet would be diminished enough that it could not make an exit hole (the short duration of the blast is a factor, too).
Vernon, Aug 16 2005
  

       I think it would be pretty clear what happened once they found the abrasive.
ldischler, Aug 16 2005
  

       [ldischler], I've wondered about that. Do ALL water jets use abrasives? How long do those nozzles last, if they use abrasives to cut through inches of steel? And how well might a water jet cut flesh/bone if no abrasive was used?
Vernon, Aug 16 2005
  

       At least you said "extremely pressurized"... Water, being almost totally incompressible, would not make a very effective jet on it's own. I've witnessed the hydro-testing of compressed air vessels at 10,000+ psi. When the seal goes, you get a "pop" and a little mist and that's it - no deadly water beam! Now, if you had a cylinder with some air behind the water, the expanding air could force the water to act as a deadly water beam...
Navy_Guns, Aug 16 2005
  

       Solid=constant shape, volume, mass liquid=constant volume, mass gas=constant mass   

       shame on you, vernon, I would have thought from your other posts that you put more thought into this type of thing.
GutPunchLullabies, Aug 16 2005
  

       For cutting inches of steel and so forth, you use an abrasive. The water jet simply carries the abrasive at high speed. Still, you can cut soft things with water alone. You could slice a banana. Or a pizza.
ldischler, Aug 16 2005
  

       [GutPunchLullabies], when you remember that you can add a fair amount various substances to water (salt) without the water level rising, then you KNOW that there is empty space in-between the molecules, which could allow for some compression of the pure liquid. Not easily, of course. But not impossible, either. Also, read up on Ice II (which unlike ordinary Ice I is denser than water).   

       Nevertheless, I agree that you may have a point, in that if compressed air was added to the cartridge, then the water jet would last longer. Whether or not it would be effective as a cutting jet remains to be determined, however.   

       [ldischler], thanks. Note that if you aren't trying to cut through the skull, you can still commit murder with this weapon by slicing the carotid or the jugular, in the neck. No abrasives needed!
Vernon, Aug 16 2005
  

       The problem is how much energy it will take to compress the water by how much. If you take the amount of energy it will take to pierce a skull, and use that to PUSH (so to speak)a 1/16 inch column of water into your storage tank, technically this should give you enough energy for skull-puncturin'.   

       However, all this energy will be quickly expended in compressing the water a very (very) small amount. the result will be that on opening a (perfect) valve, a few microliters of water will jet out at high speed, perhaps causing some pain/micropuncture at very close ranges.   

       Try putting a gunpowder charge behind a piston full of water with a narrow valve. Use a large diameter piston and small diameter hole and you will be limited only by the strength of your materials.
GutPunchLullabies, Aug 16 2005
  

       [GutPunchLullabies], check that Ice II link again. You will see that Ice II is 17% denser than liquid water, which means that liquid water should be compressible by a similar amount (say 10-15%). This means that rather more than microliters can be jetted. Heh, I thought people would be complaining about the strength needed of the cartridge, to contain the pressurized water, more than there are complaints about the degree to which water might be compressed.
Vernon, Aug 16 2005
  

       Yes, water is compressible. The ocean levels would be 40m higher if it wasn't. But the pressures you need to store even a small amount of energy are huge. That's why water based fluids in spray cans are pressurized with a gas. Use a gas Vernon, otherwise your gun will be too heavy to pick up.
ldischler, Aug 16 2005
  

       [ldischler], I modified the water-jet link and found another link regarding the ocean bottom, for comparison. I really think your compressed air won't be enough for the gun to work as intended. Do note that I never mentioned getting more than one shot per cartridge!
Vernon, Aug 16 2005
  

       Water is not very compressible.
DesertFox, Aug 16 2005
  

       I think that ldischler is right in that the compressibility of water is very small, and so the expansion volume on release of pressure is also very small. But if gas is used at 55,000psi, I think that a membrane would be needed to stop the gas dissolving into the water. Furthermore, would the gas be 'gaseous' at this extreme pressure? If not, then it might not expand quickly enough when released. I wonder if it would instantly freeze the water?
Perhaps it gives a new meaning for 'being iced'.
Ling, Aug 16 2005
  

       I think Vernon should make this weapon, use it to kill someone, then present this discussion in court to prove he could not have done it.
baconbrain, Aug 16 2005
  

       A waterjet can cut through metal, but not instantaneously. You'd have to keep the shot spot on for long enough to do sufficient damage. So as you say, execution only.   

       Furthermore, as _everyone_ else has said, water is effectively incompressible for all practical purposes, irrelevant discussion of exotic ice forms and theoretical outer limits notwithstanding. Yes, water does compress, but the structure required to do it and the minimal energy stored mean that it simply isn't worthwhile.   

       If you store water pressurized to say 50,000psi it will store some energy and exert stresses on the tank walls. If you store water and air at 50,000psi, the stresses will be the same, but the stored energy will be much higher. You'll store enough energy for a shot in a much lighter cartridge if you use gas instead of water as the propellant, as you will be able to reduce the initial operating pressure.
david_scothern, Aug 17 2005
  

       Rather than deal in generalities...   

       "one part in 5×10^7 decrease in volume for each atmosphere increase in pressure"   

       So one kilogram (liter) of ammo will eject 5 microliters of water for each atmosphere of pressure you put on it.   

       See link for better method of execution using pressurized water! (blunt trauma)
GutPunchLullabies, Aug 17 2005
  

       so... 200 atmospheres (2800psi) to expel 1ml of water? Not ideal, especially when the pressure's going to decrease from 2800psi at the start of release to 0 by the end, and must weigh much more than 1kg when the tank is included.   

       A paintball gas tank of the same sort of volume stores enough energy for about 1,000 shots.
david_scothern, Aug 17 2005
  
      
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