Now, in my world, Gauss weapons are in common use for use in armor piercing where LP (low-powered) lasers and plasma fail. Using solid steel needles, slugs, or bolts, depending on the size, shape, power, and caliber of the firearm, these weapons are highly effective for launching ammunition at high enough velocity to pierce or shatter almost any non-reactive armor, also being extremely effective against wardroids, only faltering against shields (which will be ignored for the purpose of my question).

However, how feasible is this niche in military application? The extremely basic prototypes of gauss weapons we have today (the GR-1 "Anvil" being a perfect example) aren't exactly what you'd call armor piercing. In fact, handheld versions are so low-powered that one would have to be insane to use it over a typical gas-operated firearm.

So, for the purpose of my question, let's assume there are three classes of armor: light infantry armor uses a kevlar-like fullerene fabric, with the appearance of modern-day flak armor, medium infantry armor uses a solid carbon nanotube composite, with the coverage and appearance of medieval plate armor, and heavy infantry and vehicular armor uses a carbon-titanium superalloy, with the appearance and coverage of the likes of a 40k space marine. Do note I fully expect the last one to not be regularly pierceable by most handheld Gauss weaponry, and they are not supposed to, but I'd still like to know how they'd perform.

Do note that if this niche is infeasible, do present an alternative application instead.

EDIT: Most weapons in my world often use a miniaturized onboard power source as well, ranging from nuclear reactors the size of a medium water bottle to a Penrose mechanism the size of a donut (don’t ask how it works portably, because it’s not you think). Most of the time it’s just the former though. As a result, power needs can be quite high.

EDIT2: As requested below, light infantry armor can resist smaller calibers shot from a modern gun, like 9mm, medium armor can reliably resist bullets up to 12mm, and heavy armor can take even higher calibers that are not specified because I literally cannot find one higher than 12mm. This is probably very inaccurate, as it mostly relies on rampant google searches and ChatGPT wrestling, but this would probably provide a good basis. For the reactor, once again, searches and AI wrestling, but it can produce about 5 MWs. Please tell me if any of these figures are too small or large to be feasible or usable.

EDIT3: Some additional info: the civilization using these firearms also has access to extremely cheap superconductors in the form of stable hard light, which should provide quite a bit of additional power.

  • 1
    $\begingroup$ PSA: Gauss weapons are more commonly called coil guns. At the current level of technology, man-portable coil guns are low-energy toys, with projectile energy similar to an airgun; the few experimental powerful coil guns were definitely not man-portable. (The big problem with powerful coil guns is that they are very inefficient at putting the energy in the projectile; instead, most of the energy goes into the gun itself, which is rather counter-productive.) $\endgroup$
    – AlexP
    Mar 7 at 19:43
  • $\begingroup$ @AlexP I am aware of this fact, and detailed it… actually quite vaguely. Maybe I should edit it. Anyways, I am not asking in relation to what we have, I am asking in relation to what we know. Namely, can such velocities be achieved with what we know of what is possible with magnets? $\endgroup$ Mar 7 at 20:06
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    $\begingroup$ Are you asking about a self-contained rifle/pistol, or are you open to other design options? $\endgroup$ Mar 7 at 20:37
  • $\begingroup$ @AngryMuppet I would prefer a rifle or pistol-like design, as I have some designs that I’m rather proud of for that specific layout, but I am very open to alternatives if they present an interesting design in appearance and/or function. $\endgroup$ Mar 7 at 21:03
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    $\begingroup$ How effective are the three classes of armour at resisting projectiles? For example, does the light infantry armour reliably resist current 5.56 mm or .50 BMP? Frankly, we don't care what they are made of, since we're not designing both your armour and your weapons! (At least, not in the one question.) Similarly, what are the power outputs of the portable nuclear reactors? We don't care (much) how they work, just what power there is to work with. $\endgroup$ Mar 7 at 21:05

5 Answers 5


Gauss Guns are not Electromagnetic Weapons

Despite Wikipedia's claim to the contrary, Gauss Guns are not synonymous with Coil Guns. Coilguns were invented by Kristian Birkeland, gauss guns were invented by Johann Gauss, and they work by fundamentally different principles. Gaussguns use solid state magnets, not electromagnets, so they need no significant power source. They work by using a series of magnetic balls and/or pistons (which I will hence forth just call balls for simplicity sake) space gapped by non-ferromagnetic balls. As one set collides with the next it knocks the next ball loose and that then gets magnetically drawn into the next stage in a way that creates a compounding acceleration.

The maximum speed of a gauss gun is significantly limited by the material properties of the balls. Once your velocity gets high enough to cause any sort of armor penetrating effect, the balls themselves will start being destroyed inside your gun causing a catastrophic failure of the whole weapon. So, while they make for a neat science experiment, their maximum stopping power hard caps way before you get anything resembling military usefulness.

SOURCE: https://www.researchgate.net/figure/Operation-of-a-Gauss-gun-a-Standard-design-for-use-outside-an-MRI-scanner-shown-before_fig1_282688077

You Probably Mean Either Coilguns or Railguns

Coilguns are more complex than railguns giving them more ways for things to go wrong; so, modern militaries have generally chosen railguns as the best option for military usage because reliability is so important when designing a weapon. This being the case, I will suggest if you go with an magnetic mass driver for infantry use, that it be a Railgun of sorts. However, complexity aside, both weapons have similar advantages and disadvantages; so, feel free to pick whichever you want and the below information will still apply.

Railguns can potentially accelerate slugs to much higher speeds than chemical firearms because they are not limited by the expansion rate of gasses. That said, railguns scale down much worse than cannons do because they can maintain uniform acceleration, heat, and stress across the whole barrel whereas cannons get most of thier acceleration and stress near the chamber. So while a tank and a riffle actually have similar mussel velocities despite thier very different scales, a rail gun's mussel velocity is directly proportional to how long the barrel is. So if a 10ft long tank railgun can fire at 2,500 m/s way out performing cannons of similar size, a scaled down 3ft barrel will only fire at 750m/s underperforming chemical riffles of similar size.

So, in order for your railguns to become effective anti-armor weapons in your setting, you need them to make some significant strides in material science. First of all, railguns make a lot of heat meaning you need a new kind of electromagnet that either has a way higher specific heat than modern magnets or a much higher melting temperature (or a combination of the 2). Secondly, the rails on a railgun repel each other just as hard as the accelerate your bullet. If you make the electromagnets too strong, they will literally rip the gun in half; so, you'll also need some very advanced, light weight structural materials. The 3rd major issue is of course power, but you can handwave that part with your portable fusion reactors.

So as long as you assume material science has come far enough, then there is ample reason to believe a portable railgun with faster than chemical slugs is achievable, and preferable as an anti-armor weapon.

Does this come with any unintended consequences?

Like I said, your maximum railgun speed is limited by barrel length; so, if you decide to make riffles that can fire at current naval-railgun speeds, then we can also infer that your bigger railguns are much faster and stronger too such that we can assume your tank sized cannons will fire fast enough to put a shell into orbit, and large navel cannons could even reach escape velocity (assuming your slug does not just burn up leaving the atmosphere).

  • $\begingroup$ Material science should not be a problem, since my civilization has access to very powerful materials created by what are essentially gods, not to mention they have access to cheap stable hard light. $\endgroup$ Mar 8 at 20:29
  • $\begingroup$ Is it really possible to put a shell into orbit? I have asked similar question here before trying to get the amount of energy needed and never gotten an answer. The energy loss becomes so exponential that the amount needed is like infinite $\endgroup$
    – Andrey
    Sep 25 at 20:39
  • $\begingroup$ @Andrey Stable orbits from a cannon are impossible when you only calculate for Earth's gravity and the shell's velocity because your origin point will be part of the orbital path; so, your shell would land back approximately where it started, but this is still an orbit, though be it short lived. Such a weapon could hit anywhere on the planet or a wide range of orbital targets. There are also other factors that could be used to create a stable orbit like the Earth's rotation around the Sun, atmospheric skipping, or the Moon's gravity. $\endgroup$
    – Nosajimiki
    Sep 27 at 13:31
  • $\begingroup$ That said, my point had more to do with achieving orbital speed than actually launching satellites into space from a tank sized railgun. $\endgroup$
    – Nosajimiki
    Sep 27 at 13:31

You should start thinking in joules of energy.

Handgun: 2,000 joules Rifle: 4,000 joules .50 caliber: 20,000 joules

If you can put that much energy into a projectile, then it doesn't matter what is launching the projectile; it will pack the same punch.

There are three issues with coil guns achieving this.

  1. Power generation, which it sounds like you have covered, but this is going to determine your rate of fire. 1 watt is 1 joule per second. 1 horsepower is 746 joules per second.

  2. Capacitance: storing the generated power in a form that can be quickly dumped into the coils. This is almost always hand-waved. Even in reality, we do this by increasing the charge differential across a vacuum, so this is something that's easy to elide.

  3. Transferrence: Moving the energy from the coil to the projectile. This is the part where we lose most of the energy with a coil gun, and it's why rail guns are more popular. The thing that makes coil guns so hard is that you have to shift power between electromagnets in the time between when it passes one and when it passes the next. Superconducting rings might make this interesting.

Overall, if your technology allows you to overcome the technical challenges, then there's nothing to prevent these from being effectual.

  • $\begingroup$ My civilization actually has readily available and extremely cheap superconductors in the form of stable hard light, so I would like to know what a superconductor would entail. $\endgroup$ Mar 8 at 7:11
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    $\begingroup$ @TheBenefactor, that will help a lot. The limit on field strength of the rings is the amount of power you can push through them before they melt. Superconductors don't resist the flow, so you can push huge amounts of power through a tiny ring, and space the rings tightly together, so that it provides continuous acceleration. $\endgroup$ Mar 8 at 16:49
  • $\begingroup$ Note: Gauss Guns are not coil guns despite Wikipedia's assertation that they are synonymous. The weapon described by Carl Gauss used solid state magnets, not electro magnets $\endgroup$
    – Nosajimiki
    Mar 8 at 19:03
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    $\begingroup$ Under point 3, do you mean "The thing that makes coil guns so hard"? Railguns don't have the problem you're describing there. $\endgroup$
    – Cadence
    Mar 8 at 19:05
  • $\begingroup$ @Cadence, fixed, thank you. $\endgroup$ Mar 8 at 19:58

So long as you have a means to solve the power supply and power delivery, then yes. This is very feasible.

Solid projectiles have a number of benefits that energy-type weapons don't have - mainly revolving around the need to dissipate all that kinetic energy.

Now, sure, a laser has a lot of energy to dissipate too, but with a big enough heatsink or shield or thing, it's just absorbing energy.

Whereas with a solid projectile, you have Newton's Laws of Motion - an equal and opposite reaction e.g. knockback/stagger.

Even in the real world, when someone wearing body armour gets shot by a conventional firearm, they still feel it. Scale that up to the energies a coil gun could achieve and we are talking some serious down-range effects even if the round doesn't penetrate

Then if you are using physical armor to stop it, you have to deal with things like spalling, etc.

  • 1
    $\begingroup$ It's not enough for its own answer, but in sci-fi settings you have the issue of atmospheres (or the lack thereof). Modern, conventional firearms may not have the tolerances to keep a perfect seal, could freeze up (via "cold welding"), or set high-oxygen worlds on fire. If firearms are adapted to negate these issues, they may also lose their effectiveness and gain loads of complexity. Just some things to add! $\endgroup$
    – PipperChip
    Mar 7 at 23:46

As Robert Rapplean says above, the dangerous thing is the energy. To put it another way, you could take the jacketed slug out of a bullet, swallow it and likely pass it without issue. Bullets are not dangerous any more than the ground is, but when you fall off a building, the ground becomes lethal. It is the energy being dumped in to you quickly that is dangerous.

Here are some various energies with their use cases:

~500J: light target and handgun rounds (9mm, 45ACP, 40S&W) often popular for submachineguns due to lower gas pressure making the recoil cycle easier to maintain reliably

~1500-2000J: lighter hunting/varmint rifles, carbines, modern battle rifles (5.56NATO, 7.62x39)

~2000-3500J: medium hunting/game rifles, previous century battle rifles, modern light machineguns, some modern heavier battle rifles (30-06, 30-30, .308, 7.62x51NATO)

greater than 3500J: rifles built for either large game, extreme range or are mounted/crew-served weapons .. at this point your target is typically not people, but large animals .. farther on, the target becomes vehicles, emplacements or areas to suppress e.g. the M2 heavy machinegun, mostly unchanged for 100 years, fires around 13000J

Modern armor's job is to slow down a projectile. If you are hit, you are taking that energy. The difference between a a few broken ribs with a nasty bruise and a lethal injury is how fast you take that energy. Spreading that energy impulse out just a little is very significant. Armor penetrating rounds often defeat armor by going extremely fast, even if they are lower energy.

Momentum, often represented by 'p' is the product of mass and velocity: p = m*v In order to accelerate something up to that velocity, you apply force to it. When you stop the object, that stored force pushes back. F = dp/dt .. that is the force equals the change in momentum divided by the time for that change to take place.

If you plug in the definition for momentum, above: F = (dvdm) / dt .. let's presume mass is constant (if not, you have Star Trek acceleration) F = (dvm) / dt

The force needed to achieve a certain change in speed over a certain time, or the force realized by a change in speed over a certain time, is the name of the game. So, can magnetic linear accelerators do this?

First, let's see how much force an M4 firing a M855A1 round imparts to the slug to bring it to lethal velocity:

Wikipedia lists the performance of the M855A1 FMJBT round as: 948m/s, 1859J, 4g Wikipedia also lists the M4 carbine as firing the M855A1 FMJBT at: 910m/s Wikipedia lists the M4 barrel as: 368mm (14.5in)

I'll take the above as a baseline and round the values off a bit: 900 m/s, 1860J, 4g over 370mm

We're missing the time it takes to accelerate the bullet, but we can solve for that using the definition of a Joule: 1J = kg*m^2/s^2 => J / kg = (m/s)^2 => m / sqrt(J/kg) = s

0.0037 / sqrt(1860 / 0.004) = s
=> 0.00000543

.. on to the force, now: F = (dvm) / dt => F = 9000.004 / 0.00000543 => F = 662983

.. that's a fair bit of force.

The Wikipedia article on railguns is a bit of a mess. It has a useful amount of math, but it is smeared around over various aspects of the system. I'll try to trim it down a bit. Many railguns consist of two 'rails' that a sled or armature runs between (or on top of). The sled completes a circuit between the rails. The basic idea is that a moving current generates a magnetic field, which can apply force. A lot of current will get you a lot of force on the sled, which can push a projectile.

If current is "I" and the inductance per length of the rails is "L' ", the force applied to the sled is: F = (L' * I^2) / 2

.. now it gets a tad hairy if you want to unravel that and actually compute stuff: F = ( (mu0I^2) / 2pi ) * ln( (d-r) / r )

mu0 is a constant - it is the "vacuum permeability"... kinda the effect of generating a magnetic field using electricity in empty space with no physical constraints.

I is still current, or amps. d is the distance between the exact centers of the rails, (disregarding their thickness - for now) r is the radius of the rails (presuming they are circular cylinders)

The big contributer here is I, or current. It is in the numerator and is squared.

Let's shape the railgun to be roughly the same form factor as a M4. .. let d be the width of the M855A1 round, or 5.56mm .. let r be the width of the M855A1 round, divided by approx. e+1, or 1.495315mm (0.0014953143028) there are arguments for thicker or thinner rails, and measurements that make sense, but honestly I chose this value to make the math easier.

Computing the parts we know and have decided: F = ((0.00000126 * I^2) / 6.28) * ln( (0.00556-0.001495.. / 0.001495.. ) => ((0.00000126 * I^2) / 6.28) * 1 F = 0.0000002 * I^2

So, to duplicate the force of an M4: 662983 = 0.0000002 * I^2 => 1820691 = I .. that's quite a fair amount of current.

Now, I'm doing nearly enough hand waving to take off, but that gives you a really rough ballpark measure.

I think that the picture I have is incomplete, because I know there have been railgun experiments done and I can't imagine them using that much power to get that mediocre of a result. That's what the math I was able to crib together says though, so that's what I'll go with.

So, to your actual question, how many MW do you need? Well, it depends on the number of volts. If 1 is enough, then about 2MW should be fine. I'd say hedge your bets and say at least 3.

Keep in mind that is for ONE shot, though.

If you want more penetration, that often means more energy. You can make your projectile lighter, but at some point you'll get to the point of firing a needle one molecule thick. If you want to propel a M855A1 round at M2 heavy machinegun energies or beyond, you need to scale up. It seems the force is limited by essentially the square of the current.

However! If you have this technology, there are a couple questions you need answers to, some limitations and secondary effects:

Issue: friction and strength Railgun rails undergo a massive amount of friction. They need to be electrically conductive, and that limits the materials you can use to construct them. The M4 barrel is commonly made of a chromium-molybdenum steel alloy that handles high heat extremely well, but it is about as electrically conductive as a pineapple. In fact, the pineapple, due to the water and acids in it, likely conducts electricity better.

If you scale up the power enough to have a functional railgun, there are secondary effects that are usually pretty weak, but at those power levels are evident. Railgun rails experience a very strong shear force pushing away from the armature/sled. Your rails need to also be very strong or they'll simply bend away from each other, tearing away from the sled.

Solution? magic material You mention you have superstrong armor. If your armor material is also electrically conductive, then it can be the rail material, too. Most ballistic armor works on the principle of slowing down the round rather than trying to deflect it. For instance, a metal shield will deflect a sword, but a sword can cut right through kevlar. Kevlar works by enmeshing a spinning ballistic round in a web of strong threads. The faster the bullet spins, the tighter it wraps itself up in the threads, slowing itself down.

Most materials get their 'strength' from molecular bonds. If you pick up a stick and try to snap it, the force you feel resisting you is bonds between the organic molecules that make up the stick. If your magic material was formed with sub-nuclear bonds, it might be much stronger.

Quantum entanglement is a process of getting two photons to exchange quarks. Once this occurs, measuring the spin of one photon causes the other to instantaneously (to our best measure) exhibit the opposite behavior. If a material is made that consists of molecules with some entangled particles, it might be incredibly strong. I don't know if anyone has tested, or if it is even possible, but there you are.

Effects: super strong and thin, no friction issues, conductive If this material exists, it can be expensive and limited use, but it should have other effects on society. It should be possible to build bearings that effectively never wear out and are solid. If the entangled molecules can be aligned along one surface the material should be super smooth and nearly frictionless. Any vehicle should become way more fuel efficient since this material could be used to strengthen it with little weight. If it is also conductive, it could make electronics a lot more efficient, too. The additional links between molecules of the material could make it even easier for electrons to flow, reducing resistance and impedance. If you can move electricity faster, computers also get a lot faster. One of the main issues these days is getting a signal from one side of a chip to the other side. Additionally, one of the slowest things you can do in a computer have the CPU is talk to other hardware like network cards, drives, video cards, and the like. Faster signals mean all your devices in a computer get their data way faster, too.

If you have a material that is essentially superconducting at room temperature, it might make electricity flows so efficient that railgun power requirements go down significantly. *wink, wink*

If your material is very low resistance/impedance, that could solve the next issue.

Issue: power delivery and/or storage Generating lots of power is one thing. Getting it from the generator to where it needs to go is another. A fundamental issue and a big loss of power is just moving it around. One of the issues with railguns is just switching in all the power and getting in to the rails all at once. As you saw, diameter of the rails is important. If you want to push a lot of power through a material, the thicker the material the 'harder' it is to get the power through, but the less you lose as heat. If you make the material thin, it is easier to move the power through, but if you make it too thin, you get a light bulb filament or a toaster heating element and you lose power as heat.

Solution? magic material If your super material is not only strong but conductive, it could solve that issue. It could allow the switching of a vast amount of power without resisting the flow of the electricity, losing almost none as heat while also being so thin that the power is not impeded by the material.

Effects: most of the above, but even more so! Electricity amounts required to do anything will plunge dramatically. Weaving some of this material in to wires would make delivery better. Wires of this material would carry power farther easier, meaning you need to put in less power at the front to get a certain amount at the back.

If you couple very low resistance/impedance highly conductive and strong material with enhanced power generation, power should not be a problem for anyone, anywhere. The amount of usable power from existing power generation methods would increase overnight. New electronics would require way less power, enhancing the effects of traditional generation sources. If you also have 2MW/s generators that are man-portable, then anyone can have almost unlimited power. Magnetic levitation should be widespread and common if the generators are as well. That much power easily available might also make directed energy weapons feasible. You might also hit the edge of the ability to synthesize matter at low scale. If you can put a 2MW generator in every soldier's weapon, having a few tens of Mtons per second of power and superconducting wire available might allow the creation of matter from energy. It wouldn't be fast, it would likely be pretty slow and painstaking, but it might be possible.

  • $\begingroup$ A room-temp superconductor is already canon in my world in the form of hard light, which also happens to be cheap. As for the super-material, I should be able to work that out rather easily, as nanomachine-forged meta-alloy, while of varying advancement throughout my timeline, is a common sight in military applications. Also, as for the whole more effective electronics thing, my civilization has access to a far more advanced form of computation. $\endgroup$ Apr 11 at 18:15

If by gauss weapon you mean a hybrid system between a coilgun and a chemically propelled projectile than yes you probably could do such a thing with the only caveat being timing between the coils switching on or of and you could not use a ferromagnetic material for your barrel (though I’m kind of unsure about that one as I would assume it could cause a catastrophic malfunction by tearing the barrel out of the gun) the projectile you fire would first be propelled by the propellant in a cartridge before the coils would accelerate it down the barrel this would allow the use of a conventional weapons system without the weapon becoming a bomb with the massively increased pressures required to reach though velocities normally and while the weapons could be rifled they would experience rapid wear and tear with the increased speed as the friction between the barrel and the projectile would likely melt the barrel after a few shots unless some kind of ceramic or tungsten foam was used along with active cooling systems to account for the heat load or solve the problem of the friction between the barrel and projectile


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