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I'm building a sci-fi world in which there are a lot of wars, fought across the galaxy. In order to make this world feel real, I want to design weapons that are well-suited for the environments they'll be used in.

In this case, I want to design a weapon that will stand up to the microscopic dust particles found in places like the Moon and Mars. To do this, I'd like to know what sorts of problems modern Earth weapons (specifically automatic rifles) would face. For instance, what parts of the weapon would face problems, what would those problems be, how long would it take before the weapon would be rendered inoperable, and are there any possible solutions?

I would like answers to be based around real-world science, experiments, and experience, rather than pseudoscience and guesswork.

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    $\begingroup$ Cave Johnson here! We grounded those rocks up and made a gel from it. Gives you cancer. Who'd have thought the eggheads wouldn't see that coming... $\endgroup$ – dot_Sp0T Dec 5 '16 at 18:13
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    $\begingroup$ Guns and middle east deserts. Have you investigated it? It seems we have a lot of data avaliable :) $\endgroup$ – Mołot Dec 5 '16 at 18:40
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    $\begingroup$ @Mołot Moon dust is much finer than normal sand, thus it presents a more unique challenge. $\endgroup$ – DaaaahWhoosh Dec 5 '16 at 18:44
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    $\begingroup$ @Molot Here is a distribution of moon dust particle sizes; and here is a presentation of earth soils. Almost all moon dust is less than 0.01 mm, and the majority is below 0.001 mm. Sand is considered .05 mm or larger, silt is .002 mm or larger. So most moon dust is very fine by earth standards. $\endgroup$ – kingledion Dec 5 '16 at 19:29
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    $\begingroup$ I started doing research to answer this question only to be taken down a terrifying rabbit hole of an argument fought with the zeal of console wars by people who own several fully automatic firearms. I no longer feel safe. $\endgroup$ – Sidney Dec 5 '16 at 20:54
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Dust is going to be a big problem for anything with moving parts. Moon dust caused all kinds of havoc with the Apollo missions, getting all over every surface, causing respiratory problems, destroying equipment. Moon dust is incredibly sharp and abrasive, and because of UV bombardment it is also electrostatically charged, meaning that it wants to stick to everything and is almost impossible to get rid of.

It's also chemically active. After three days on the moon, Apollo 17 astronaut Harrison Schmidt had to throw away his geologic hammer because the handle had corroded away.

Hatches, seals, valves, bearings—any machinery that moves on the lunar surface will be subjected to dust damage. “Imagine sprinkling broken glass onto a seal,” said Gentry. “And then every time you cycle it, you sprinkle more glass. Sooner or later it’s going to leak.”

The dust on Mars is slightly better in that blowing in the wind wears off some of the sharp edges, but it is even more chemically active; the Red Planet is red because of iron oxide, and Mars certainly contains other mineral oxides and peroxides, which can cause chemical burns. The Pathfinder rover also found trace amounts of carcinogens like hexavalent chromium in the soil.

So any weapon you make with moving parts is going to have trouble in these environments.
There is an answer to this though: Metal Storm

enter image description here

A Metal Storm gun is made from multiple barrels, each packed with bullets that are fired electronically in a series.

enter image description here

There are no moving parts, no firing pin, there doesn't even need to be a trigger. Each barrel could be sealed right up until it's fired, and then once the gun is empty you replace the barrel with a full one. The rest of the gun could be made out of ceramics and other materials that resist corrosion and abrasion.

enter image description here

More on dust and the effects of dust

So there is no atmosphere or weather on the moon, so stuff shouldn't move around much, right?
Well no.
When the Apollo missions visited the moon, they left reflectors behind, and over the time since these reflectors have begun to degrade, which kind of baffled scientists; no wind to blow dust, and the degradation has worsened over time so it's not just dust that was thrown up when the astronauts left.
The degredation is also worse durring a full moon than it is when the face of the moon is in shadow.

Scientist now believe that when the solar radiation hits the dust on the moon it knocks off electrons, ionizes it, giving it a positive charge, and since like charges repeal, the dust particles push away from each other, with some lofting as far as tens of kilometers above the moon's surface.
When the sun sets the solar wind delivers electrons to the moon, deionizing the dust and causing it to fall, and sometimes lofting new dust as patches get negatively charged.
The further into the 14 Earth day "moon day" that you get, the more charged the dust will be, causing it to grow stickier and stickier.

So even without wind or people stirring it up the dust keeps moving around.
With people moving around, rockets landing and taking off, etc. it's going to be much worse.

Any new moon base will have to be planned out carefully, to keep launch facilities far away from science and living facilities.

There is also the problem of dust and electronics.
Dark lunar dust can prevent excess heat from radiating off of delicate electronic components, causing them to overheat.
The spray of debris caused by the Eagle's departing rocket motor led to the overheating and early failure of Apollo 11's Passive Seismic Experiment (the first major scientific experiment put on the moon by human hands). Electrostatically charged dust can also potentially carry enough of a charge to shock unprotected electronics.

Toxicity and Health
Not much is known about how toxic dust is simply because no one has been exposed to it for very long.
It has been shown to at least cause respratory problems in astronauts in the short term, but long term effects are unknown and will need to be studied as we someday move back to the moon.
Vision is another area where dust will be a problem, since the dust is essentially microscopic jagged shards of glass, iron and unsatisfied chemical reactions. Scratched cornias are a potentially serious problem.

Mitigation One interesting aspect of lunar dust is that microwaves can melt lunar soil in less time than it takes to boil a cup of tea. A future vehicle employed on the moon could therefore melt the dust into roads and launchpads. This would help reduce the amount of dust thrown up by people and vehicles on the lunar surface.

Alternating electrostatic fields in airlocks could be used to draw the dust away.

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    $\begingroup$ Devils advocate here, these may suffer the same heating problems traditional firearms would face in an airless environment and adding electronics makes far more vulnerable to dust. $\endgroup$ – John Dec 21 '16 at 16:55
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    $\begingroup$ Both the barrel and the body could be sealed against dust, and you could possibly transmit the fire command from the body to the barrel using induction, so no exposed electronics at all. As to heat, you fire however many rounds and then pop out the barrel. That's probably not enough heat to warp the barrel. And you could set up some kind of cooling system that taps into the suit to pull the waste heat out of the gun. $\endgroup$ – AndyD273 Dec 21 '16 at 17:18
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    $\begingroup$ the two systems are mutually exclusive, either the gun is sealed or you swap out the barrels. Warping is not as a big a problems failure due to heat. Weight will not be much of an issue so you can make the barrels heavy, but heat transfer will still be an issue. Don't get me wrong I still think this is the best solution it just needs to be thought through. $\endgroup$ – John Dec 21 '16 at 18:40
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    $\begingroup$ @John I can picture where the barrels can be swapped out, while the gun stays sealed, simply because they are two separate parts: The barrel and the receiver. The receiver holds all the electronics and stuff, while the barrel holds the bullets. The receiver is sealed tight, and the barrel has a dust seal over the mouth. The barrel is slotted into the receiver and held tight by some kind of clamp. After the barrel is empty the clamp is released, the barrel drops out, a new barrel is inserted, and the clamp is reengaged. In this kind of gun you wouldn't need much of an upper, since nothing moves $\endgroup$ – AndyD273 Dec 21 '16 at 19:41
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    $\begingroup$ I can see that working, having near vacuum between the barrel and the rest of the gun over most of its length will cut down on the heat transfer as well. kinda rules out precision rifles though, if your barrels swaps out you'll need to realign a scope with every swap which will take a few shots leaving not much left in the tube. $\endgroup$ – John Dec 21 '16 at 21:02
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Moon dust a problem for guns? Moon dust is going to be the ammo.

On Earth, stuffing some sand into a cannon and firing it will produce a large cloud of disappointment. Air drag on individual particles will quickly bleed away the kinetic energy, slowing and dispersing them before they travel very far. So for people whose enemies are not cooperating by standing at the end of the gun, carefully-sized projectiles are used which tightly (but not too tightly) fit the barrel, allowing them to get maximum acceleration from the gunpowder charge before exiting the barrel, and then suffer as little drag as possible on their way to their targets. The barrel needs to be kept tolerably smooth, less gas escape around the bullet, or rough areas cause it to bounce around in the barrel on its way out. The barrel is sometimes rifled to encourage the bullet to spin, so that air resistance doesn't affect its flight path as much.

On the moon, with its lack of atmosphere, this calculus changes dramatically. With no air resistance, small projectiles will have as much range and accuracy as large ones. And moon dust is sharp. Stuff some into a blunderbuss and you'll have a combination sniper rifle/shotgun that'll rip through spacesuit fabric like wet paper.

Yes, it'll corrode the barrel rather quickly; that will cause some dispersion, but plenty of dust will still be expelled at maximum speed straight forward. Particularly for close-range combat, you won't have much trouble until the barrel gets thin enough to be at risk of exploding.

Of course, your dust gun won't have much penetration power against armored targets. For those, as Andy alluded to, you'll want conventional(ish) projectiles and disposable barrels.

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  • $\begingroup$ Moon dust has particle sizes in the micrometer range. Being so small and with so little mass, normally neglected forces like static electricity would affect it, as would even the Moon's negligible atmosphere. I don't think that will work. $\endgroup$ – kingledion Dec 5 '16 at 19:31
  • $\begingroup$ @kingledion An ounce of moon dust has as much mass and static charge as an ounce of bullet. It'll be an effect, but not a big one for most of the dust coming out. Though if you're concerned, just wet the dust with some salt water to ground it to the barrel. $\endgroup$ – Sneftel Dec 5 '16 at 19:33
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    $\begingroup$ An ounce of bullet is solid, which means that a) it does not disperse itself in flight due to repulsion from electrostatic forces and b) it does not spread over the target's surface on contact. The kinetic energy of a bullet penetrates the target, the kinetic energy of your weapon would slightly sandblast the target. $\endgroup$ – SJuan76 Dec 5 '16 at 19:45
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    $\begingroup$ @Sneftel Wetting the dust with salt water will not work. The water will evaporate. $\endgroup$ – Taemyr Dec 5 '16 at 20:42
  • $\begingroup$ @Taemyr It doesn't need to stay wet. Moon dust doesn't build up a charge quickly. $\endgroup$ – Sneftel Dec 5 '16 at 20:55
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Air

As a general rule, ordinary firearms would fire without trouble on the Moon, on Mars and in outer space. Gunpowder includes it's own oxidizer so you don't actually need air to fire one. This is why firearms an shoot underwater. All other chemical explosives will continue to function for the same reason.

Temperature

The biggest problem is heat dissipation. Firearms generate lots of heat and cool themselves through contact with the air. If you're fighting in a low-air environment you'll need to add some cooling system to it. This system should eject waste heat material (perhaps in the form of steam) so that the heat does not dissipate into the user's suit or accumulate in the heat sink.

The other thing to worry about is cold. Steel brought near absolute zero by the vacuum of space is more fragile than it is at room temperature. For extremely cold environments you will need to make firearms out of other metals or materials that hold up better against the cold.

Other than this, temperature shouldn't be too much of a problem. If a human can survive it a rifle can too. Heat gradients shouldn't be much of an issue either because they're dependent on the amount of heat generated by your weapon, which stays constant whether you're firing on Earth or on Pluto.

Dust

You can bury an AK-47 underground for years, clean it off and it'll fire just fine. More advanced weapons like the M16 tend to jam up in dirty desert conditions. The AK is cheap to manufacture and easy to repair, so if the dust problem is too bad you can just seal it in a plastic bag and use it as a disposable weapon. If you're in a clean environment like a spaceship then any firearm will work just fine.

Aquaeus Environments

One place you wouldn't ever want to use firearms is underwater (or other liquids). The bullets won't travel very far and the shockwave could damage the user. (Firing a gun underwater is a quick way to make yourself deaf.) In this case, you'd be better off with torpedos or melee weapons.

Manufacturing

The hardest part of using automatic weapons might be in acquiring the resources to manufacture them, specifically gunpowder. Gunpowder is a mixture of sulfur, charcoal and potassium nitrate. Our charcoal comes from fossil fuels so if these people are fighting somewhere that was only terraformed recently they will need a different method of manufacturing it. This isn't impossible for a spacefaring civilization (they can grow trees if they lack creativity), but it's something worth noting.

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I’m amused at old sci-fi that has spaceships and maybe FTL but otherwise is exactly WWⅡ technology. They use slide rules, and any computers are huge room-filling machines that can barely compute an orbit when tended by a staff of experts. No microwave ovens, no composites, no plastic.

So, you postulate a galaxy-spanning civilization and can make war economically.

But everything else is exactly like the civilization and technology that the author is familiar with today?

Imagine if a medievial (pre-gunpowder) author tried to envision “world war” spanning contenents, complete with 20th century sized battleships and aircraft. What kinds of spears, axes, lances, bows, etc. would be suitable for an “intercontenental war”?

A firearm similar to what is made today is the same kind of thing. Remember the lessons of spinoff technology (microwave ovens, radar, microelectronics) that go along with your postulated technology of galaxy-wide travel, and updated materials (plastic, composits) that go with a more advanced technology base.

So firearms made of carefully fitted metal parts with fine tolerances, need for lubrication and cooling, and expensive/precious so not disposable: that’s so 19th century!

Just like we have plastic foam cups and carbon fiber tennis rackets, they will have nanobot utility goo, programmable matter, superatoms, etc. Instead of solid machined metal parts, they will have biology-analogue items made of nanobot “cells” that clean themselves just like living things, sweeping out small particles and repairing microscopic damage automatically.

Materials will have physical properties that make cooling a non-issue: superconductors of heat, and materials that not only take the heat build up but use that to reclaim energy as it slowly cools down again.

But will you even have firearms? Nanoprojectiles in an airless world can launch thelselves without “guns”. They won’t punch through the suit with raw kenetic energy; they will digest the material and eat through dumb matter, and hack enemy smart matter or otherwise disrupt it using techniques that go with its principles of operation—that is, poison the suit material or enemy equitment so it stops being able to clear particles and repair itself (and is then vulnerable to being digested/disassembled).

Why fire a projectile or projectile delivery system at all, when the very regolith they walk on could become a swarm of nanobots that engulfs anything that touches it?

You might not be blasting each other with high-energy lasers, but instead beaming more subtle Bluetooth-like signals to hack the opponent’s systems and nanobot building blocks. Tell his suit to remove itself, or that the sensor readings for life support are wildly wrong.

In fact, using a primitive dumb-matter projectile might be an unexpected tactic that takes them off guard.

But why send ground troops to fight on a body like the moon? Drop a rock on them or use a ship’s drive, and end of enemy installation. Weapons of mass destruction will be commonplace adaptations of spacefaring infrastructure.

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  • $\begingroup$ "nanobot utility goo, programmable matter, superatoms", you are so 21st century ;-) $\endgroup$ – Henning M. Dec 3 '17 at 18:05
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There are a couple of considerations. While a modern style automatic rifle would work on the moon, you will run into problems with using them in warfare.

How are they aimed while in a space suit? You are not going to have the dexterity to pull a trigger very well with pressurized gloves. You are not going to have an easy time shouldering the rifle and aiming an optical sight through a faceshield. So you are going to need a smart aiming system that uses a camera that relays an image to an in-helmet gunsight. Fortunately this is somewhat trivial and mostly been solved already.

Heat dissipation is an issue. Modern weapons get hot FAST with full automatic fire. But you won't have an air-cooled affect. Shedding brass helps a bit, but if you go caseless then you have even more heat build-up. So now you need a liquid cooling system or elaborate radiator fins on the barrel. Heat is a problem because it will reduce the lifespan of the barrel and potentially "cook-off" a round sitting in a hot chamber. You can work around this with a rotary barrel like a gatling gun (less effective in an airless environment), or an open bolt system that keeps the ammo out of the chamber until the bolt drops to fire (look at an old machine gun like a Thompson SMG, for example). You can also have a cooling element included in the ammo or running along with it like a belt-fed ammunition system.

You also have to consider the wide fluctuation in temperature form the cold state at rest to hot from firing (as well as in shadow or exposed to sunlight). A lubricant that can function in those extreme temperature ranges would be a good one indeed, unless your firearm comes with an HVAC system. A dry carbon based one like graphite may be an option, or you could design the weapon out of materials that are designed to abrade itself and don't expand/contract with temperature (ceramic, perhaps). Again, this trades immediate functionality with increased maintenance costs as the gun literally wears itself down with use.

Dust is handled in several ways. On Earth, you can try to seal the gun or open it way up. Dust adheres to the lubrication material used to smooth metal-on-metal contact or via electrostatic forces. Trying to open up the gun design so it has loose tolerances and lots of gaps for junk to fall out probably won't work well in an airless environment (and some would argue doesn't work well on Earth, look at the complaints of about the open slide Beretta pistol in desert environments). But it does seem to help the AK-47 series work in austere environments.

Sealing the gun up is also possible, so no outside material can get in. Problem here is that nothing can GET OUT. So your ammunition has to be clean and over time little metallic shavings from the operation of the gun itself, as well as from the cartridge, in addition to powder residue and primer residue, will accumulate, requiring maintenance in a clean room. And any opening, for ammunition ejection or whatever, is a vulnerability.

Recoil management may be an issue, depending on how the gun system is mounted on the lunar soldier. It would probably be mounted right over the chest so recoil is inconsequential, as opposed to hanging out way off to the side on a shoulder mount, for example. But you can incorporate internal mechanical recoil compensation like on the KRISS Vector submachine gun. Probably not the best idea to redirect escaping gasses from the cartridge to compensate for recoil as that would just blow up lunar dust or strike nearby surfaces. As it is you will have a plume of gas, partially consumed powder, and primer residue in front of you.

So on the moon, with ultrafine dust that can stay suspended for prolonged periods of time, a combination of an external sealed case and internal loose tolerances ought to give enough reliability for sustained encounters. But such a rifle will need it's own cooling systems in order to maintain a high rate of fire, and will probably also need sealed ammunition boxes. And an electronic aiming system. And temperature regulation. And maybe recoil compensation. That means the weapon system will start to resemble a small vehicle more than a conventional rifle. It can't be serviced well "in the field", there are specialized techs back at base to keep everything up and running, and the gun downtime is probably much higher than the uptime.

You may save yourself a lot of headache if you go with something more like a pneumatic rifle. With no atmosphere and very low gravity, lots of the features of modern rifles may not be necessary. Rifling to impart a spin, firing in an upward arc to compensate for gravity, etc. Compressed gas or even a hammer strike might propel a projectile with enough velocity to penetrate an armored suit (presumably such things exist) at the ranges folks can see each other. You could even have a penetrator flechette that rides a sabot out of the barrel, or the old gyrojet concept. Point is, the tried and true assault rifle may not be the optimal tool with all of the reworking you'd have to do for a lunar environment, even if you don't want lasers or rail guns.

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I have a bit of a passion for firearms, and there's a few things to keep in mind:

For one, for a fire arm to work in space, it would need to inject the oxygen necessary for the powder to ignite and explode into the chamber. This is hardly impossible, but it would be far too complicated for a reliable, cheap to manufacture weapon's platform.

Consider that on the Moon there's little to no atmosphere, and very, very low gravity. This means that projectiles will experience little friction once fired, and also that they will not experience nearly as much downward drag as they would on Earth. The result is that projectiles will lose little speed, and altitude, even over long distances. Suddenly, a 9mm carbine can become a deadly sniper rifle!

There's a couple of other things to also consider. On the Moon, everyone needs to wear relatively fragile space-suits in order to survive. This means that in order to kill your target you need simply to penetrate and damage their suit, or its systems, not necessarily do great harm to their body (the vacuum will take care of that).

And so, simple air rifles are more than sufficient in achieving your goals. (simple is a bit of a misnomer - there are some very powerful air rifles out there, which could easily take down a moose, let alone a human being)

This is important to note, because you are now simplifying the firing mechanism specs, and ammunition design considerably, and the simpler a weapon is, the more likely you are to be able to build it to last, or at least make it cheap enough to replace easily.

Moon dust is indeed very harsh, and likely to jam up any sophisticated firearm (modern firearms have very small, finely machined, and tightly fitted together parts which would be prone to failure as "sharp" dust particles get jammed in). However, a relatively "crude" air rifle need not be sophisticated at all.

In fact, you could manufacture millions of them, each one rated for maybe one or two outings before having to be seriously serviced, or simply replaced. Alternatively, you could make these things out of some sort of very advanced ceramics, which are highly resistant to corrosion.

Watch a few videos about firearms such as the Kalashnikov, or the SKS carbine. Specifically, look for "torture testing" videos. These things can be dropped in ankle deep mud, or buried in sand, picked up, cycled, and fired, without even properly shaking the dust/muck out. A similar design, but cycled using compressed gas (nice and cheap), would increase reliability, and make them almost perfect designs for the lunar surface.

A note here, is that you may wish to add blow-back valves to the designs, such that a weapon will vent the pressure in case of a catastrophic jam, rather than blow up in the operator's hands. And since moon dust is apparently electrically charged, you may wish to make these firearms out of a material which you can charge to repel those particles (should be possible with modern material science/engineering).

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    $\begingroup$ Gunpowder doesn’t use air. If you’re saying the primer does, then just use a different primer or other technology for initiating it. $\endgroup$ – JDługosz Dec 21 '16 at 16:06
  • $\begingroup$ agreed you don't need to inject oxygen you use normal ammunition, they work just fine an vacuum , I really want to know about the moose airgun, I know of ones powerful enough for medium game, I know of none for large game. $\endgroup$ – John Dec 21 '16 at 16:10
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    $\begingroup$ @JDługosz - yes, you can get creative and set the ammunition off electrically, etc., however you are over-complicating your weapon design by making ammo a potential point of failure. Plain metal (or ceramic) slivers are easier to manufacture, and are not going to potentially fail at a critical moment, whereas a cartridge case may become corroded, or worn, and fail when fired, creating a jam, or worse. I really don't think that there's a good case to be made for using traditional ammunition on the moon. $\endgroup$ – AndreiROM Dec 21 '16 at 16:13
  • $\begingroup$ @john - there's .45 caliber air rifles which have been proven "deadly" to a human at 600 yards or so (can punch through a certain thickness wood panel - used to be the standard military yard stick for penetrating a human breast-bone). They are used in hunting medium game, as you said, and have some claim to be able to take down much larger game with them as well (based on shot placement). $\endgroup$ – AndreiROM Dec 21 '16 at 16:15
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    $\begingroup$ This is my test comment, for the purposes of obtaining a secret hat. $\endgroup$ – AndreiROM Dec 21 '16 at 17:25
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Swap out the guns every couple of years.

Moon dust is not that big a problem for a purely kinetic machine that is only cycling a few thousand times a year under the worst circumstances. Modern firearms are very robust machines made from very hard metals. Plus the gas discharge may actually help keep the gun clean. quite a bit of gas leaks around the projectile as it travels down the barrel, is suspect this will help prevent barrel wear. Most military firearms are designed to cycle just fine while covered in far worse abrasives. Most of the problems with apollo revolved around seals, electronics, optics, and biology. Things with microscopic parts or air tight fittings which firearms will not have.

Scopes and optics on the other hand will have problems with "frosting". disposable lens might be a solution.

Jason was right that overheating will be a bigger issue, on the moon the gun is only cooling via radiating heat, which will be slow, which means sustained fire will not work. You will see a lot more focus on a single well placed shots. Thick barrels and adding some radiators would be a good idea. In a typical firearm about 30% of the energy from firing is converted in to heat in the firearm. With radiative cooling only that means it will not take many shots for the barrel to reach unsafe temperatures. Worse it will transfer far more heat to the rest of the firearm, the gun itself may become too hot to handle. This report has a good chart for barrel temperatures

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Modern ammunition work in vacuum. The propellant in the cartridge has its own oxidizer so it'll fire.

To make it somewhat more protected from the moon environment though, I'd say your best bet would be to use caseless ammunition weapons. There is no need for ejection in caseless weapons, so the entire receiver can be sealed tight against the dust.

Of course caseless ammo have their problems, which are why they weren't adopted back in their heydays of the 90s, but you can solve/handwave these away with technology.

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Some sort of small, open/exposed rail gun perhaps?

This would require considerable advances in that area of technology, which I don't think is too much of a stretch given you're talking about space faring civilisations.

Have the rails and magnets exposed and use electromagnetic fields to guide projectiles into place rather than having them driven by a magazine spring, this could avoid a lot of exposed (dust vulnerable) moving parts and direct contact between surfaces.

Recoil could be a problem. Maybe you could transfer the recoil energy into small flywheels somehow and have said flywheels slowly regenerate the gun's battery.

A revolver setup might be an option too, or going for another sort of technology some sort of pneumatic gun system might work.

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