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I want to know the pros and cons of hand held rail guns versus coil guns. They will be given to infantry who can easily lift the weapons. If need be they could have twice the strength of a normal human via cybernetic enhancements. What would be the various pros and cons, especially in rough terrain?

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    $\begingroup$ I've had the same question myself and ended up going with coil guns. Jim2B gave a good answer summing up my reasons. However, if you want to be realistic, you need to come up with a small, portable, hugely powerful power source for the gun. Both guns require huge amounts of electricity to fire. To fire at a typical machine gun rate (600 RPMs), you are going to need that huge power source multiplied by 600. Also note if such a power source existed, there are many, many other weapons and devices we could have. $\endgroup$
    – DrZ214
    Oct 16, 2015 at 5:11
  • $\begingroup$ what about using either of them as a sniper rifle style system to produce a long distance shot wth out the light produced from a normal gun $\endgroup$
    – madokk
    Mar 9, 2017 at 19:01

6 Answers 6

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In short (links to follow as I find time to put them in).

Coil guns (aka Gauss guns)

Have a higher max projectile velocity. Powerful switches alternate the electromagnetic poles in the drive coils as the projectile passes through the coils. This requires high voltage, high amperage, high speed electrical switches. Researchers have been trying to build these for decades with only moderate success.

is a type of projectile accelerator consisting of one or more coils used as electromagnets in the configuration of a linear motor that accelerate a ferromagnetic or conducting projectile to high velocity.1 In almost all coilgun configurations, the coils and the gun barrel are arranged on a common axis.

Coilguns generally consist of one or more coils arranged along a barrel, so the path of the accelerating projectile lies along the central axis of the coils. The coils are switched on and off in a precisely timed sequence, causing the projectile to be accelerated quickly along the barrel via magnetic forces. Coilguns are distinct from railguns, as the direction of acceleration in a railgun is at right angles to the central axis of the current loop formed by the conducting rails. In addition, railguns usually require the use of sliding contacts to pass a large current through the projectile or sabot but coilguns do not necessarily require sliding contacts.2 Whilst some simple coilgun concepts can use ferromagnetic projectiles or even permanent magnet projectiles, most designs for high velocities actually incorporate a coupled coil as part of the projectile.

The force the projectile leaves on the weapon is it attempts to compress the coils (you'd get recoil similar to a normal weapon).

Magnetic fields are not inherently dangerous to people as long as they don't have magnetic metals on their person. Other than the difficulties with switches, a coil gun is much more suitable for use by unprotected humans (e.g. infantry):

Video at link: Man portable coil / gauss gun

Railguns

Are much easier to build from a technological perspective. Current runs down one "rail" through the conductive base of the projectile and back up the other rail. This is the brute force method of electromagnetic projectiles.

A railgun is an electrically powered electromagnetic projectile launcher based on similar principles to the homopolar motor. A railgun comprises a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail.

The forces applied to the railgun try to rip the rails apart. The recoil from the projectile also supplies a recoil like a chemical slug thrower.

Each rail conducts high voltage and amperage current. Touching or getting close to one of the rails would be exceedingly dangerous. This weapon is probably not suitable for infantry use.

Video at the links:
Artillery equivalent railgun
Man portable railgun

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    $\begingroup$ An infantry railgun would have the rail system enclosed. The big problem with them is the ferocious wear on the rails (not just from friction but from high current erosion as well) which makes them require frequent maintenance and given to sudden decreases in performance is the maintenance is not done. They would also kick because you can't beat the conservation of momentum. $\endgroup$ Oct 16, 2015 at 1:13
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    $\begingroup$ Coilgun rounds also have the problem that they must have certain magnetic properties (if you don't use sliding contacts). Railgun shells need only be conductive, as the current flow itself creates the necessary magnetic relationships. $\endgroup$
    – Nohbdy
    Oct 16, 2015 at 7:44
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    $\begingroup$ Well could the infantry carry around extra rails? They would replace them after a few shots or so and continue use. Or with a covered rail system is that entirely unfeasible. $\endgroup$
    – Sunspear25
    Oct 16, 2015 at 11:55
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    $\begingroup$ Laser rifles don't work well for several reasons: 1) chemical explosives pack more energy than batteries and can release that energy faster. 2) Most lasing materials are horribly inefficient - producing way more heat than coherent light. 3) Laser optics will be severely degraded or even destroyed if mud or other debris gets on them (such debris absorbs more laser light than the normal optics and can destroy the optics. At least for the foreseeable future - no lasers for infantry. $\endgroup$
    – Jim2B
    Oct 19, 2015 at 3:03
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    $\begingroup$ @dmckee - For the same projectile weight and muzzle velocity, coilguns and railguns will have the same recoil. $\endgroup$ Mar 9, 2017 at 19:39
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While using rail or coil guns as infantry small arms is problematic (due to the various issues already discussed), there may be a place for railguns as a man portable anti tank weapon.

Current ATGM's generally use shaped charge warheads to actually penetrate the armour (the rocket motor just gets it there), and various techniques have been developed since WWII to defeat these types of warheads, including spaced armour (such as the "cages" around modern tanks), explosive reactive armour (the brick like devices attached to the outside of most Russian tanks) and even counter missiles like the Russian "Arena" or Israeli "Trophy" systems. Hypervelocity "darts" (Armour Piercing Discarding Sabot Fin Stabilized; APDSFS) fired from tank cannon are much harder to defeat, and using current or near term technology the only practical means of defeating such rounds is plates of high strength and density armour.

A tank cannon is a huge piece of equipment, firing large 120mm rounds and having massive recoil, so you need the tank to carry it around and use it effectively.

A man portable railgun would resemble a recoilless cannon:

M-40 106mm Recoiless Rifle

The propellant charge would not be used to drive the round, but rather energize a MHD generator with the jet of high velocity gas exiting the venturi, while the long barrel will house the rails which actually drive the projectile. The actual projectile can be rather small and relatively light, since the damage is delivered in the form of kinetic energy. A small projectile moving fast enough could conceptually be able to engage helicopters and aircraft as well, although a very advanced sighting system and mount capable of rapid movement of the weapon will be needed.

The downside of this weapon will be much like regular recoilless cannon: the jet of the driving charge (in this case driving the MHD generator) will certainly alert any enemy of where you are, and you will need to leave immediately after firing.

Still, this would allow light infantry to be able to take on tanks on a more equal basis, as well as defeat most types of fortification (blasting through bunkers and buildings with relative ease), so something along these lines may be considered as the technology of railguns matures.

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  • $\begingroup$ en.m.wikipedia.org/wiki/… using an explosive ferromagnetic generator would create the effect you desire without the need for superconducting hardware like mhd generators, it is also most likely cheaper. $\endgroup$
    – Efialtes
    Jan 24, 2021 at 2:24
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One advantage of a rail gun would be if you ran out of loads but still had power you could just jam the rails against and enemy and pull the trigger. The impedance would be higher, causing the voltage between the rails to be higher.

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  • $\begingroup$ lol, what an idea XD That would work too . . . $\endgroup$
    – J Sargent
    Oct 16, 2015 at 2:00
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They both differ from conventional weapons in that they use electromagnetism to propel the projectile rather than using an explosive charge. Both of them need incredible amounts of energy, which is why they are not practical in an infantry weapon at the moment. The gun barrel and mechanisms do not need to be massively heavy, the problem is supplying the power.

The advantages of rail guns is that they are much simpler to build and operate than a coil gun. They are also more powerful as they have a direct contact between the projectile and the rails while the coil gun has a gap between them.

The advantage of a coil gun though is that the coils can be insulated from the outside world more easily, which could well make them more reliable in the long run. It will be harder for external conditions to interfere with the coils and the coils will take less wear and tear in use. Rail gun rails in particular are subject to a lot of wear even from normal use.

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    $\begingroup$ They are most definitely not "essentially the same weapon". @Jim2B's answer explains it in more detail, but in essence: coil guns are way easier to build than a proper rail gun. Both can be insulated very easily, but you fail to mention to wear railguns experience. because of extreme currents? Downvoted. $\endgroup$ Oct 18, 2015 at 19:51
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    $\begingroup$ @IsaacWoods They both use electromagnetism to propel the projectile, the difference is in how that force is applied. This means both have similar requirements in terms of energy, no need for propellant, etc. My final sentence also said "the coils will take less wear and tear in use". $\endgroup$
    – Tim B
    Oct 19, 2015 at 8:14
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    $\begingroup$ While they both use electromagnetism to propel the projection, the coilgun uses straightforward magnetic attraction to pull the projectile through the barrel (the fact that it's an electromagnet is actually almost irrelevant), whereas the railgun uses the Lorentz Force to propel the projectile along the barrel. Also, in a coilgun, the coils take no physical wear and tear, whereas a railgun can only take a few shots before you end up with something like this: princeton.edu/~romalis/PHYS210/railgun/DSC01190.jpg $\endgroup$ Oct 19, 2015 at 19:43
  • $\begingroup$ @IsaacWoods I've re-worded it. Hopefully that's more to your liking. $\endgroup$
    – Tim B
    Oct 19, 2015 at 19:49
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Railgun for one they can fire faster because the rails do not need to be deactivated. Also, with a coilgun you need capacitors which can fry easy. So railgun is my preferred choice.

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    $\begingroup$ Do you not need capacitors for a railgun? All of the designs I've seen involve them. And what makes you say that railguns can fire faster? The coils in coilguns turn themselves off as the projectile goes through them, so what are you talking about? $\endgroup$
    – Kevin
    Mar 30, 2017 at 19:48
  • $\begingroup$ You do not need them but it saves power to have them. $\endgroup$ Dec 5, 2017 at 13:46
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    $\begingroup$ Then presumably you could also not use capacitors for a coil gun at the expense of power, which makes the point moot right? And either way, in what way does a railgun fire faster? As far as I understand both could be set up to fire quickly given enough energy, but the railgun would actually overheat far before a coil gun would $\endgroup$
    – Kevin
    Dec 5, 2017 at 23:54
  • $\begingroup$ You could use flywheels as a safer alternative to capacitors. They are whats used on the EMALs to charge up the em catapult. en.wikipedia.org/wiki/Flywheel_energy_storage $\endgroup$
    – Efialtes
    Feb 11, 2019 at 13:54
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A coilgun is more efficient and needs less maintenance, there is no need for as high currents, and the rail itself won't get damaged as easily. Coil guns however typically need complex control mechanisms to turn the coils on and of, this makes them a lot more fragile and reduces their maximum launch speed. While a good coilgun needs less maintenance on a small scale, a large scale one might easily break so is not as reliable in big warfare. For infantry however a coilgun likely is more reliable due to the lower power usage, and them being able to not be affected as much by things like mud etc.

Not long ago I have been working on a new type of railgun which needs no complex control things like a normal railgun, and also can reach the high speeds, yet which reaches the efficiency of a coilgun, and so requires less maintenance to things like molten rails etc. However given current events it is better if I do not explain how it works, because someone might use it against people. I also don't know if discussing such things would even be legal in a place like this since it would be like handing over a blueprint to a high power high efficiency weapon.

But since this is a worldbuilding discussion place, you can still use them, it is possible even if you don't know exactly how it works. Also you might look to different more fun things like shooting liquid/molten metal. A friend an I once designed a lava shooting gun, such a thing is more a science fair project in practice since it has more of a cool factor than actual use (relatively expensive per shot, low range, and it just shoots very hot scary stuff but if you think about it, a single bullet likely is more dangerous). However in storybuilding such things can be rather cool. It is also something which was very easy to build in real life when you know what kind of methods to use. Extending the range is also doable using water to form explosions caused by the instant boiling but such a weapon realistically only really makes sense in a story where for example you have a super hero, or some evil person who likes to see people suffering and who for example uses it in huge bombs, or if there are specific creatures which heal very fast so that it keeps boiling them for a while. You could combine something like that with a coilgun or railgun and make it boiling metal. however it all depends on your story and how far it must be to what is used and known now, since if it needs to be stuff which is doable now, then a lava gun is just a science fair project which looks cool and keeps doing damage for a while after hitting.

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  • $\begingroup$ Where did you get the lava for the lava gun? $\endgroup$
    – Daron
    Mar 28 at 19:28
  • $\begingroup$ @Daron it was not actual lava, from in the earth, it was just a molten metal substance at temperatures similar to or above lava, it was generated using a chemical reaction which is actually quite commonly used in a specific form of industrial welding. however you should not try to build it yourself unless you really know what you are doing and do so for a scientific reason. such things can easily go wrong with a small mistake and might be considered illegal. if you want to do it out of scientific interest then you should be able to reproduce it with the information I just gave $\endgroup$ Mar 28 at 20:36
  • $\begingroup$ Cool, thanks! Though I'd be more worried about burning down my house than accidentally creating forbidden substances. No one will find out. $\endgroup$
    – Daron
    Apr 2 at 15:07
  • $\begingroup$ that is true, especially for something which can be made with such basic materials when you refine them yourself. $\endgroup$ Apr 7 at 23:33

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