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This question is inspired by my the realization that the guns in my world might have problems if someone tried to fire them while they are wet. The predominate propellant in my setting is a metalloid based alchemical compound that reacts to an electric current rather than heat or agitation.

When the trigger on a gun is pulled, a mini-dynamo is spun, producing a current that is conducted into the round igniting the propellant;some guns use batteries instead.

What I wonder is how to insulate my guns so that they could be fired safely when wet.

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    $\begingroup$ Based on "a mini-dynamo is spun producing a current that is conducted into the round igniting the propellant", I'm not seeing any aspect of your design that requires exposing the electrical components to the outside environment in the first place. Wouldn't the dynamo be fully internal, with current conducted to a pair of contacts at the rear of the chamber, with some leads at the back of each round to interface with the contacts? Should be generally safe and functional, unless the electrical resistance of your water is extremely low (in which case the weapon would simply not fire until dry). $\endgroup$
    – aroth
    Commented Feb 23, 2016 at 8:21
  • $\begingroup$ @aroth I don't have a lot of engineering knowledge so I couldn't be certain. My concern was that if there was water in the barrel of the gun that it could cause the weapon to short out. $\endgroup$
    – Trismegistus
    Commented Feb 23, 2016 at 10:54
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    $\begingroup$ It could, depending upon the conductivity of the water, the resistance of the circuit through the projectile, and the design of the interface between the power source and the projectile. However there wouldn't be a safety risk even if it did short out. Or rather, the only safety risk would be that the weapon you're trying to fire isn't going to fire. Which might be a non-issue or a very big issue, depending upon what you're shooting at and why (and how angry it is at you for trying to shoot it). $\endgroup$
    – aroth
    Commented Feb 23, 2016 at 11:25

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There are two scenarios to consider here: firing the gun while submerged, and firing the gun while it is just wet.

Don't worry about making it possible for the gun to be fired while submerged. Bullets are made to fly through air, not water. The Mythbusters found a few feet of water can stop bullets even from high-powered rifles and that a fish tank can stop a shotgun blast (strictly one-time-use, though). So guns, while submerged, are only effective at point-blank range.

What about the gun being wet? To reference Mythbusters again (because I can), they attempted to build a stun gun that could use water to conduct electricity to the target. They had a lot of difficulty doing so because it's quite hard to propel water in a continuous stream (it breaks up into lots of droplets).

Given that your gun is using electricity to ignite the propellant, the firing chamber must be insulated from the grip. Thus, the only path for the current would be to go through the barrel, around the outside, and back to the grip.

Now think about what a gun is going to be like when it's wet. It's not going to retain a layer of water all over the gun - most of the water will fall off, with some water sticking to bumps and crevices. This isn't going to be enough to conduct a small amount of electricity from inside the barrel of the gun all the way out to your hand.

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  • $\begingroup$ Regular bullets are made to fly through the air, but that's not to say it's impossible to make ones that fly through water. Both flechette-type rounds and supercavitating rounds have been developed that are effective under water, though ranges are lower than those for airborne bullets. $\endgroup$
    – ckersch
    Commented Feb 23, 2016 at 22:28
  • $\begingroup$ @ckersch good to know. Though, if you have the opportunity to get special underwater bullets, you'd likely be able to get a gun that is designed for underwater use. $\endgroup$
    – Rob Watts
    Commented Feb 23, 2016 at 23:02
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It shouldn't be a problem, especially with the "magic" tag involved.

First, water isn't the greatest conductor of electricity. Even with a lot of salt in it, making it much better, it's still not that great.

Second, the electric charge will tend to go through the path of least resistance. If you have a high-charge positive and a floating ground connecting to the same system, and those electrodes are a couple millimeters apart, the path of least resistance will be from one electrode, directly to the other.

A little current may spread out and hit the user, especially since they're presumably wet and therefore grounded. But it should be minuscule. You can make a lot of the parts out of polymer, Glock-style, to mitigate the amount of current "escaping" the electrodes. (The electrons can't just run straight through the receiver, but instead have to run the long way around via less-conductive water.)

There's a video on YouTube of a guy putting 120V electrodes into a bucket of water, then sticking his fingers in the water. On his normal fingers, he was able to practically touch the electrodes before they shocked him. On his finger with an open cut, it was more noticeable, becoming painful half an inch away.

With salt added to the water, it didn't bother his normal finger until he again practically touched the electrode, although his cut finger he could only get a couple inches from the electrodes before it was painful. He was able to light an LED by sticking it in the water near the electrodes with salt, but not without.

Another YouTube video shows a guy activating a taser through distilled water with another guy's hand in the middle. Despite the hand being in the path of least resistance, there's no effect because the distilled water has so much resistance with just a couple inches of water to go through. After pouring a bunch of salt in (same video, advanced a couple minutes), there's a noticeable shock, but it doesn't send him into convulsions or anything.

If you're using a lot less than 50k volts, and/or doing it for only a tiny fraction of a second, I doubt it would have much effect.

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  • $\begingroup$ I used the magic tag because i mentioned "alchemy", my concern was whether or not water would cause the electrical system of the gun to short out,or possibly shock the wielder. $\endgroup$
    – Trismegistus
    Commented Feb 23, 2016 at 11:22
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    $\begingroup$ @Trismegistus: You'd definitely want to water-proof any sensitive electronic components, but as long as water isn't inside the switches themselves, no current will flow until the switch is flipped on purpose. Think about an electrical cord running through a water-proof grommet to the outside of your house. As long as the cord isn't plugged into an outlet inside the house, no amount of shorting it from the outside will have any effect. And the water had no effect on the guy turning a lightbulb on while immersed in water, so you shouldn't have misfires with proper voltages. $\endgroup$
    – MichaelS
    Commented Feb 23, 2016 at 11:35
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    $\begingroup$ I am making the assumption the propellant itself is insulated from the water, like a modern cartridge. The electrodes in the receiver would touch contacts on the cartridge, and any airgap spark would be inside the sealed cartridge. If your propellant is just hanging out, covered in water, it might be difficult to set it off while wet depending on whether you need an airgap (bigger airgap is harder to set off), and whether the propellant starts a chain reaction once a little is started (the chain reaction makes it easier since you just need current through a tiny portion of the propellant). $\endgroup$
    – MichaelS
    Commented Feb 23, 2016 at 11:41
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Simple answer if this "metalloid based alchemical compound that reacts to an electric current..." conducts electricity. One could forgo generating a current external to the cartridge, and simply generate the current inside the cartridge. A moving magnetic field generates a current in a conductor, that's how the dynamo works. There is no reason to generate the current outside the cartridge, thus it is sealed against water.

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  • $\begingroup$ Cartridge needs to be non-ferromagnetic. $\endgroup$
    – Seeds
    Commented Feb 23, 2016 at 21:58
  • $\begingroup$ Another poster had brought up the solution of the magazine containing everything the projectile needs. And I will go with something like that for more advanced and expensive weapons. But that brings to my mind another question, what was the hammer striking the round in the chamber do? Does striking make a small dynamo spin to produce a current, or does it shatter a dam causing the halves of a binary compound to mix creating a current. The latter would need excellent isolation against external vibration to reduce the chance of an accidental detonation. $\endgroup$
    – Trismegistus
    Commented Feb 24, 2016 at 23:41
  • $\begingroup$ The whole reason for a hammer, in firearms, is to either strike a spark or to cause enough mechanical stress to ignite a primer. In your "elect-arms" there is no need for a hammer/striker, as your current can be controlled by a switch. $\endgroup$
    – Seeds
    Commented Feb 25, 2016 at 17:14
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Nothing you have said suggests that the electrical components have to be in contact with the environment outside the gun at all. Enclose your power source in whatever airtight apparatus you want, and make sure the holes that have to exist in that airtight package are sealed with something that resists water penetration.

Depending on the technology level, wood is a pretty good insulator. It's used in transformers across the world as the scaffolding that holds the wire cores in place for exactly that reason. Fill the wooden container with a non-reactive oil if you want, or leave it as open air. Block the holes that inevitably must exist in the box for components to reach in or out with something that resists water penetration like tar or sap.

Or if the technology is better, use plastics and gaskets.

Your weapon does suggest a scene where someone tries to use a damaged gun underwater and depending on how much current you need for your compound to react, gets electrocuted. :)

Good luck!

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That is the whole reason for cartridges in the first place for weapons using gunpowder. To Keep the powder dry they made 'water-proof' capsules to hold it. So for your case it will be similar, you already have a 'bullet' holding the powder. Now you just need to insulate the dynamo and the bullet maybe with some ceramics to better control the electric charge. Don't need it to fire from a static shock! But if the 'spark' generator was inside the shell, like a spark plug inside an engine, moisture shouldn't be a big problem.

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  • $\begingroup$ Putting the spark-maker inside the round was something that hadn't occurred to me. My initial thought was that the gun generates the current which is channelled into the contact on the round, which pass the current into the propellant. The fact that the conductor is exposed to make contact with round is what prompted the question. If the gun was soaking wet or under water and someone fired it what happen? The round containing everything brings up the question "what sort of generator is inside and how is it triggered". $\endgroup$
    – Trismegistus
    Commented Feb 23, 2016 at 17:15
  • $\begingroup$ Well the gun would still create the charge, like in a car, but the 'spark plug' would be inside the cartridge/ $\endgroup$
    – bowlturner
    Commented Feb 23, 2016 at 17:38
  • $\begingroup$ So in your design the gun only supplies the power. Everything else is inside the Round? $\endgroup$
    – Trismegistus
    Commented Feb 23, 2016 at 20:36
  • $\begingroup$ yep makes sense to me! :) $\endgroup$
    – bowlturner
    Commented Feb 23, 2016 at 20:37

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