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Flamethrower and other incendiary weapons often use several liters of fuel and due to this they are easy targets and dead weight in an army. Additionally flamethrowers that use fuel have limited uses. This problem could be solved by getting rid of the fuel entirely and only relying on electricity.

  • This weapon does not need to shoot flames but merely cause flames to erupt at a given point.
  • It does not need to be usable at long ranges but should be at least usable at a distance of 5 meters.
  • The tech level should be modern day.
  • This weapon should be relatively portable
  • The weapon can use air and should be reusable.

So how could a fully electric incendiary weapon work?

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  • $\begingroup$ If the goal is just to make fire at the target location without all the downsides of a flamethrower, not to make a cool lightning gun, modern militaries have solved the problem already. Put a small explosive charge and a flammable substance in a container. Deliver and trigger it by all the normal ways of delivering and triggering explosives. $\endgroup$
    – g s
    May 13 at 3:44
  • $\begingroup$ @g s This seems like a full answer, and if so, should be posted as an answer, not a comment. $\endgroup$
    – Bubbles
    May 13 at 4:28
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    $\begingroup$ "several liters of fuel and due to this they are easy targets"..."flamethrowers that use fuel have limited uses": a battery that stores a similar amount of energy to a tank full of fuel is going to be quite volatile, look at how lithium ion batteries react to abuse while containing a fraction of the stored energy. Additionally, a battery has to store both components used in a chemical reaction, while a fuel can be burned with the surrounding air. And it's a lot faster to refill a tank of fuel than it is to recharge a battery, reversing the chemical reactions involved in its discharge. $\endgroup$ May 14 at 12:01
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    $\begingroup$ A bit confused what you want with "The tech level should be modern day." Contemporary militaries don't have electric plasma flamethrowers, so... it seems like the answer is 'there isn't one'. $\endgroup$
    – Kaia
    May 14 at 19:23
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    $\begingroup$ I don't think you've thought through the benefits you hope to achieve. Chemical fuels are much more energy dense, both volumetrically and per mass, than any current battery technology. Especially more so than known battery technologies that don't carry at least as much risk in the event that they are breached. Switching to electric makes the weight, target size, and risk much worse, even if you could produce desirable effects electrically. And the "limited uses" that flamethrowers have are exactly the uses they are wanted for, which cannot easily be delivered electrically. $\endgroup$ May 15 at 13:57

11 Answers 11

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Plasma Torch

The closest option to a flamethrower would be a scaled up plasma torch. The operation is relatively simple: as air is pushed out though a nozzle, the electrodes in it create an arc that ionizes the air. As the ionized air exits the nozzle, it produces a jet of plasma that is hot and forceful enough to cut steel.

Given that the use of a plasma torch is very similar to the combustion based acetylene torches, it should have roughly the effect you desire. However to achieve the range and scale, you'll have to scale up the gas/air flow and the arc current.

The biggest obstacle (to this and all electric designs) is the power source, as batteries are less energy dense than combustibles. If you're after a flamethrower tank, then that's less of an issue as they could have MW's of electrical energy to throw around, but man-portable weapons will have problems (baring a Mr. Fusion or similar).

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  • $\begingroup$ If you don't mind me asking what would the range/heat of such a weapon look like? $\endgroup$ May 13 at 14:05
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    $\begingroup$ Without extra physics-defying tech, range of such devices is generally measured in centimeters at most. The heat they deliver is intense, many thousands of degrees C, but jets of very hot gas also dump heat into the air immediately around them with very little directionality, which makes it YOUR problem very quickly as you scale up. Liquid flamethrowers launch fuel that is ignited at your barrel-tip, but most of the burning happens far away from you. Plasma torches do all the burning in your device, then send the rapidly cooling/diffusing result in some direction. $\endgroup$
    – Jay McEh
    May 13 at 15:23
  • $\begingroup$ @Coolcats112 Commercial torches appear to operate somewhere around 20 000 °C, ±5000 with ranges of centimetres. The thrower would likely use a much higher gas flow with barely ionized air (unclear, but google suggests ~5000K) to get better range with as little self heating as possible. Unfortunately, this gets into too much fluid dynamics, thermodynamics and rocket (engine) science for me to know how much range we could get before self-destructing. $\endgroup$
    – jb6330
    May 13 at 16:37
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    $\begingroup$ @jb6330 The range problem is a product of your projectile, not the torch itself. Jets of liquid can stay more or less laminar for some distance, but gases can't be fired at any appreciable range in a line or even a cone--they very quickly become a cloud. This is true in a vacuum and even worse in an atmosphere, and the more excited your gases are the more eager they are to go in effectively random directions. Honestly I'd worry less about the device itself overheating and more about the ambient temperature cooking the user if we try to scale up much beyond a cutting torch. $\endgroup$
    – Jay McEh
    May 13 at 17:49
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    $\begingroup$ A lot of semisoft scifi gets around this by saying their plasma stream is enclosed in "magnetic braiding" or other wording that all essentially boils down to cylindrical forcefields fired like a laser, with a chewy plasma center. This is fine and fun, but from an analytical perspective the potential applications of that kind of magitech field manipulation makes the plasma filling about as silly as mounting a flint arrowhead to the tip of a thermonuclear ICBM. $\endgroup$
    – Jay McEh
    May 13 at 17:53
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It cant

The problem you have is of power generation, storage and discharge - as per my comments to Isoentrópica - if you are using a projectile weapon - then there is little to no advantage over using a conventional firearm with special ammunition. e.g. Dragons breath for a Shotgun or an Incendiary grenade from a Grenade launcher etc.

So if you arent using a projectile weapon, you need a way for the electricity to get from point A to point B - which you have said is a distance of 5 meters. We are talking about a lightning Gun of sorts.

Now, quick aside - full confession - Rule of Cool - Lightning Guns are cool, impractical and with current tech impossible - but still - freaking cool.

looking for data online - I see one reference to about 4 MV per Metre to arc a gap. so that is 20 MV or about 4,000 times what a Taser is putting out. That is a lot of voltage.

I will now do another aside - I am not an Electrical engineer - but my understanding is you can have a whopping high amount of Volts but it without a corresponding Amperage, it is not going to do Squat - and so to get both enough Volts to arc across to a location (We will get to that in a minute) and have enough Amps to do nasty things on the other end - you will need something close to a portable power plant.

And then there is the location - Whilst a Flamethrower is notoriously indiscriminate (if it Burns, it Burns), Electricity will arc onto whatever is closest and provides a path to ground.

You could point it at your desired location, activate the machine and for nothing to happen because there was a steel rod stuck in the dirt off to your left that you did not see.

Now - if you move away from todays Tech Levels and add in some handwaivium, you can get something that will kinda work - but as you have laid it out - completely impossible.

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    $\begingroup$ @Coolcats112: What about them? $\endgroup$
    – AlexP
    May 13 at 0:44
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    $\begingroup$ @Coolcats112 - I mean, if you want a Laser - that is not an electrical flamethrower... that is a laser. However the core problem of Power generation, storage and discharge applies. $\endgroup$ May 13 at 0:47
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    $\begingroup$ I am an electrical engineer. Simplifying things, amps kill, voltage doesn't. A million volts backed by a milliamp is only one watt (voltage x current = power) and while such a spark would scare the b'jeebers out of you, it wouldn't kill you. We can use water as a metaphor to demonstrate the point. A very thin stream of high pressure water (voltage) might cut you, but unless specifically applied, it won't kill you. On the other hand, anchor yourself at the bottom of a tank and slowly fill it with water (amperage) and you're dead as a door nail. $\endgroup$
    – JBH
    May 13 at 5:29
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    $\begingroup$ @TheDemonLord I made a mistake with my math. Sorry about that. A million volts with a microamp is a watt. With a milliamp it's 1,000 watts. Less powerful than a household hair dryer... but at least enough to kill. I hate being imperfect... it's so inconvenient. $\endgroup$
    – JBH
    May 13 at 7:23
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    $\begingroup$ @JBH - I may or may not have added the Caveat that I wasn't an Electrical Engineer because I may or may not have thought that someone who frequents SE:WB is and may or may not come along with the correct maths.... $\endgroup$ May 13 at 7:33
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A Rose by Any Other Name...

You want a flamethrower that isn't a flamethrower. Strictly speaking, that can't be done. The value of a flamethrower is that it can deliver combustion to an incombustible area. For example, a concrete bunker.

Could you do that with a tool that (ignoring electricity) remotely combusts things? No. Nothing inside the concrete bunker other than what was brought for the purpose of the bunker is combustible. If it's a machine gun nest, then the ammunition is combustible, but how would that be ignited by a remote heat generator? And if you could ignite it, you wouldn't be igniting all the ammunition at once but only that ammunition that fell under the "beam" of the weapon.

Worse, a remote heat generator of any sort (electric, laser gun, solar optics, etc.) can only work line-of-sight where a traditional flamethrower fills the space with combustible material.

Conclusion: Not viable

Flamethrowers don't just throw flame. They throw a burning substance. WWII flamethrowers used a stable substance like diesel fuel. If you pierced the tank with a bullet, it actually wouldn't explode. Have you ever tried to burn diesel fuel by just setting a match to it? I have. It takes forever to burn away. But convert it into a spray and it burns quite readily. Coat something with that spray and whatever is coated burns. Without the ability to coat something with a combustible material, you don't have weapon that solves the problem flamethrowers were invented to solve.

Note #1: piercing the tank of a flamethrower is dangerous when the flamethrower is in operation. It isn't dangerous (more accurately: not as dangerous) when it's not in operation. Without a substantial nearby ignition source, the fuels used in combat flamethrowers are very stable.

Note #2: commercial flamethrowers, like those used to burn weeds, use liquids like propane that become a gas when emitted. Faster heat, lower range. This might be the type of flamethrower you're thinking about where the damage is very local (less than one meter). You still can't do that with electricity. But at least it would be more believable from a suspension-of-disbelief perspective.

Brutal honesty: you're proposing a large spark plug as a replacement for a flame thrower. An electric discharge requires a termination point that's lower potential than everything else around it and there's no practical (or meaningful) way to create that lower electrical potential remotely. This is why electric discharge weapons don't work today as a means of offense.

Caveats: You could use an electron emitter as a directed energy weapon, but that means you're delivering charge, not necessarily heat. A strong enough electron beam could start a fire. It could cut through the concrete... however the battery required to do that is much more dangerous than the tank of combustible material. For one thing, it's a lot heavier and on the other, disrupting an energy storage device of that size has dramatic consequences.

Note #3: I can't underscore the problem of the battery enough. You could hand wave it, but the truth is that the rules of physics are brutal. Casting energy for the purpose of bulk damage requires a lot of energy and batteries simply stink at that. And when they're pierced by gun fire, they have a much higher chance of catastrophic discharge, which doesn't require a nearby ignition source.

Electricity is great for point solutions such as tasers or rail guns where the electricity is used entirely locally. But given today's technology, it's useless for direct remote attack of any form.

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  • $\begingroup$ Your comment about electron emitters sound very much like low-wavelength coherent radiation. That (to me) sounds like a nice path to achieve what OP wanted. However, I am not sure whether e.g. X-rays can generate sufficient heat in a target... or if it's practical at all considering that X-rays are already harmful because they're ionizing radiation. $\endgroup$ May 13 at 7:01
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    $\begingroup$ @Isoentrópica Part of the problem is that the OP is trying to replicate the behavior of the weapon while ignoring the purpose of the weapon. Using electromagnetic radiation could create a three-dimensional field that would cause damage like a flamethrower, but only for the period of time the EM field is in play. Turn it off and the damage turns off with it. Once a combat flamethrower has doused its target, the soldier can walk away while the target continues to burn. Frankly, a bazooka firing phosphorus rounds is a better match. $\endgroup$
    – JBH
    May 13 at 7:21
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    $\begingroup$ @Isoentrópica to me it sounds like electron beam welding. A great way to cause a lot of local heat with a limited energy budget. Sadly you need a vacuum to avoid beam dissipation. Also focusing to counteract electrostatic bloom would be a challenge. $\endgroup$ May 13 at 12:14
  • $\begingroup$ There are plenty of handwavium applications of force fields and portals and whatnot that could let this concept work... but doing so is like using Star Trek transporter tech exclusively to ease loading a single trebuchet. The intermediate developments required make the final objective absurdly moot. $\endgroup$
    – Jay McEh
    May 13 at 15:37
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    $\begingroup$ @JayMcEh You're absolutely right, except for the OP's bullet #3 binding answers to contemporary technology. $\endgroup$
    – JBH
    May 13 at 18:44
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Fire guns

This might be cheating a bit, but one possible solution is loading bullets with flammable liquid that ignites upon impact with the target. There are plenty of compounds that can ignite spontaneously, and this technically fulfills your requirements. However, these bullets are likely almost as dangerous to you in storage as they are to whoever you are shooting them at. If something goes wrong, you get a face full of fire, and possibly(probably) explosions, although this could be a plot point itself. A bit more of a "technically", but gets the job done.

EDIT: This also reduces on fuel, as you need less fuel to set something on fire assisted with the energy of a bullet than you do to actually shoot flame. Probably only a few mL per shot. This reduces the fuel that has to be carried around significantly. Also, It is less likely to detonate from environmental factors(assuming the bullets are made properly) and if some do go off, it will likely be contained unless to many go off at the same time.

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  • $\begingroup$ This sounds like it defeats the point OP wanted to make — that of getting rid of fuel as a vulnerability in warfare. As you said, it also sounds very dangerous to lay around... $\endgroup$ May 13 at 6:57
  • $\begingroup$ @Isoentropica There is a lot less fuel, and the lower quantity also makes it a bit safer. Plus it is less likely to detonate from nearby flames or other environmental factors while it is in the bullet, if the bullet is made well. It would have to be directly breached for it's payload to go kaboom, and you would need several of them to make a big enough fire/explosion. Significantly safer. $\endgroup$
    – Bubbles
    May 13 at 13:39
  • $\begingroup$ @Isoentrópica If you contain the load of hypergolics within a thin metal shell that leaves the barrel like a bullet, significant forces will be needed to break the complete round with its brass propellant container and only the tip of the bullet sticking out. But the bullet would safely break upon impact due to the sudden strong forces from the front without anything around its sides to stabilize its side walls. $\endgroup$ May 15 at 6:54
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Lightning guide.

Still in the experimental phase, there have been real experiments with laser to create channels of ionised air that could trigger a static discharge from a cloud above.

In your case you would have to force a little bit the technology because it could be easily neutralised with a lightning rod. In any case they would work only in rare situations. But in a surprise attack it could be devastating.

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I think you've got 4 options:

  1. Incendiary grenade. Lob it at a target, and you set it on fire. It still uses fuel to create the fire, and if you shoot the grenade instead of lobbing it, that also uses fuel of course.
  2. Heat ray. This was my first thought: if you want something to burst into flame without throwing something at it, you're going to have to heat it. Archimedes figured this one out.
  3. Laser. Lasers are a great way to transfer heat over very large distances. They do use a lot of power if you want to heat something quickly, though.
  4. Shoot lightning at it. Not sure how controlled this can be. Probably the worst option.

I do need to point out that making a target burst into flame by itself is hard and requires a lot of heat. Archimedes used massive mirrors and had wooden targets. A lot of material won't burn so easily, or at all, and will melt before it bursts into flame. Flamethrowers are effective because they take a shortcut: they cover the target with flaming substance. Also a practice that goes back to at least the middle ages, if not longer. There are different ways to deliver that flaming substance: a flaming jet from a flamethrower, an incendiary grenade, lobbing flaming projectiles at the target, and possibly more. You get the best effect if the flaming substance is sticky, so it sticks to the target while burning. Merely using electricity without flammable substance won't set everything on fire. But you could heat it until it burns or melts.

I realise now these different methods really have different goals: using flaming substance (flamethrower, greek fire) uses the flammability to heat up the target and cause it damage. Heating the target until it bursts into flame turns that around. But is the fire the goal? Or is it the means with which you accomplish a different goal? Maybe heating something until it burns is only really feasible when you've got easy access to lots of heat (big mirrors and a sun) and your target is flammable enough that it will spread the fire by itself once it's hot enough to burst into flame.

Fire is cool, but not always efficient.

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  • $\begingroup$ There's a story in the Bible about a guy who used incendiary animals with little torches tied to their tails to burn all of some city-state's crops. Not very PETA-friendly, that guy! Possibly the first record of the use of guided missiles in warfare? $\endgroup$
    – g s
    May 13 at 23:22
  • $\begingroup$ @gs not just the Bible, the Russian Primary Chronicle also contained a story of Olga taking tribute off some tribe in small birds, then after collecting, she tied small fires to those birds and released them, to ignite their straw roofs. The tribe then got wiped IIRC. $\endgroup$
    – Vesper
    May 14 at 6:56
  • $\begingroup$ @Vesper That's one of my favorite myth-histories! She agrees to marry the guy who killed her husband and took over his kingdom, but only if he gets everybody in his part of the country to send her one of the birds that roosts in their roofs as a wedding present. So when her servants set all the birds free with slow fuses burning on their legs, they fly back to their nests. $\endgroup$
    – g s
    May 14 at 7:05
  • $\begingroup$ the wiki article on "greek fire" has notes on its use (7th century onwards) and that there were other, less amazing, alternatives used before it. So "cover the target with flaming substance" indeed goes way back! $\endgroup$
    – Syndic
    May 14 at 9:50
  • $\begingroup$ "making a target burst into flame by itself is hard" Very hard if the target is made out of concrete or stone or Hescoes full of sand or, etc. Those things still can be damaged by intense heat, but all of the heat has to come from the weapon. The stuff they're made of won't destroy itself for you. $\endgroup$ May 14 at 18:37
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I don't think you can replace a flamethrower with something else. Yes, you could probably throw something that was its own oxidiser, such as dioxygen diflouride. Fluorine will give horrible burns that poison and do not heal. Flamethrowers were mostly instruments of limited range. They only shot a few tens of meters. Something like 2/3 of the deaths in the trenches were from artillery. You could hear artillery, but you could always hope that it landed somewhere else. Everyone could see the flames. Everyone could imagine the horrible death that would ensue. But flame-throwers could only shoot 10 meters or so with the wind in the right direction.

Then came the Livens Large Gallery Flame Projector. That could fire over 100 meters. It weighted two and a half tons, and was 15 meters long, and was assembled underground. It would burst the surface, and shoot 300 litres of fuel in three 10-second bursts. And that was it. Maybe 6 months of fuel for a family car. That won't turn the course of the war in a battle where the allied forces lost 57 thousand in the first morning. And yet it might have done. These were only deployed in the south of the battlefront. Most of the intelligent use of mines and saps was in the south, and that was where all the gains in territory happened.

How did that work? If you were in the German trenches, you would have seen the jet of flame. Here around the 40-minute mark is a reconstruction of what that would look like. You would have gone down to your dug-outs, which were properly underground and safe. When you came back up, your trench would have been occupied by enemy troops from a parallel tunnel.

Other things killed with a transparent spray. Poison gas did that. But a visible flame cleared dug-outs like nothing else. You can't make a 'nice and clean' flame thrower: blatant in-yer-face evil is how it works.

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Remove fuel Uses electricity.

You get how electricity is just a different type of fuel, right? To weaponize electricity you typically need a large power source, which, interestingly enough is also just as at-risk of blowing up, is heavy or cumbersome, and is basically just a delivery system of energy with the purpose of killin'.

All that being said, you can make it even more cumbersome and outlandish. Wear an aluminized suit that if you tear it puts you at risk of taking an air bath with an air fryer. Take a backpack, fill it with batteries and hook it up to some buck converters. Also carry a tank of compressed air and a long tube. Radially ionize the air using HV caps hooked up to coils as it goes through a tube 'flamethrower style' and then push it into a bunker or other area with a fan and wait awhile, when the air is sufficiently ionized you give everyone a huge static shock by swapping the polarity of the electrode.

(none of this is how physics or electricity works btw, it just sounds good on paper until you get here.

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Most electrical fires are caused due to overheating of electrical components, which could be achieved by Joule heating: a high resistance, high power component can be shorted with an intense current.

Your weapon of choice could use short-range ammo that contains a charged, isolated capacitor besides a high-power resistor. These cartridges could activate when in contact with a body, which would trigger their contact and make the resistor heat and explode very quickly. This could start a fire very easily.

For higher power, you could also include in the cartridge a metal that burns very easily (e.g. magnesium), rolled around the exploding resistor.

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    $\begingroup$ Why would you use this weapon over a 12 gauge loaded with Dragons breath rounds? $\endgroup$ May 13 at 0:09
  • $\begingroup$ @TheDemonLord (I didn't know what a dragon's breath round is... You do learn something new every day.) I think the main advantage would be remote activation: while dragon's breath fires exactly from the gun it's shot, Joule heating ammo would detonate in contact with a body which opposes sufficient mechanical pressure. $\endgroup$ May 13 at 0:20
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    $\begingroup$ I admire the enthusiasm, but if my choice is between taking a 12 gauge that can fire lots of different ammo and some special contraption of only marginal effectiveness - I know what I am taking. $\endgroup$ May 13 at 0:22
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    $\begingroup$ Actually, what you're suggesting is a technologically complex (and therefore expensive) replacement for much cheaper phosphorus munitions. While usually used to create smoke screens, they've been used for direct attacks due to the phosphorous entering the body and burning when the oxygen in the body contacts it... causing significant heat damage (and it's hard to remove). It's now a treaty/human rights violation to use it in this way (Source). $\endgroup$
    – JBH
    May 13 at 5:46
  • $\begingroup$ Thank you @JBH — that is another piece of warfare I didn't know about. I have just realized how impractical creating an electrical fire would be, since it's just igniting a reducing agent (like magnesium or phosphorus) but with extra steps. $\endgroup$ May 13 at 6:56
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The conductivity of air is a problem here. According to wikipedia you need about 10,000 volts for every cm of air. This would take huge amounts of power just to jump the gap and it would expose the shooter to possible arcs as well.

But that could be overcome with a little imagination. If you permit to use a little "fuel" you could first spray a thin mist of some conductive fluid, followed by a large shock as soon as contact is made. Basically a taser with more steps.

Alternatively, we could make use of the fact that air becomes conductive as soon as it is ionized, i.e. becomes a plasma. Plasma is not that hard to make: a candle flame is plasma, as well as the spark between to electrodes. Using some unknown tech you could first enlarge this plasma, then accelerate this towards the target and then have a large discharge as soon as contact is made. Again, a taser with more steps but now now fuel is used except for electricity.

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Incendiary paintball rounds. Get your average paintball gun and have it fire paintballs loaded with your flammable substance of choice - maybe napalm? Ignition is trickier, but you might get somewhere by having a tiny charge inside some or all paintballs, or phosphorous-based incendiary coating as is used in tracer rounds.

A quick search says gasoline has 36.4MJ/L and a .68 caliber paintball round has a volume of about 2.7mL, so a single paintball can deliver 98kJ of potential heat energy in gasoline form. A full-auto paintball gun can fire 30 times per second and can deliver its payload to a target well past 5m.

It's not fully electric, but you get a thing that can "cause flames to erupt at a given point"

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