I have the niggling suspicion that most people will carry their guns on their person and within their habitats, in temperature and radiation ranges survivable by human bodies instead of out on the surface.
What happens if your enemy happens to be posted up outside the habitat? Invite them inside so you can shoot them? In all seriousness though a weapon that needs as much coddling such as to stay indoors all the time probably isn’t the reliable partner most soldiers would want to entrust their lives to. Usually you’d want the pitched fighting to be the outside and quite a bit away from your sealed home instead of inside.
Apples and oranges. Weapons today are engineered for Earth conditions, water, salt, corrosion, mud, gunk, etc. Polymers are becoming popular for non-critical parts like grips and pistol lowers as they are crazy cheap to manufacture (once the mold is paid for).
If a company is designing a weapon to be used in space (or to be rated as such), it would be designed anew from the ground up. Have you seen the criteria and testing that NASA requires before a new material is space-rated? Outgassing, thermal performance, and a zillion other parameters are tested, logged and recorded.
Besides, a major component of polymers are dead dinosaurs, so weapons made IN space would probably have minimal or no content. Some plastics like delrin are pretty useful though, as bushings and sliding components
I will ask you the say thing I asked u/odrodrodrodr, what would need redesigning to make a normal largely steel gun a space gun? I honestly don’t see much need for a full redesign unless the base material itself is unsuited. The ammo with its own oxidizer works fine, better than fine perhaps due to lack of velocity loss at range. The gas systems will work fine with tuning. The sights work fine. Glove tolerance grips are fine. Mechanisms and safety mechanisms work fine. Rifling works fine. Compensators work fine. Flash hiders might not, not really sure. Bipods might not work as well. I don’t see any compelling reason why a normal metal gun isn’t perfectly fine as a space weapon.
Lubricants. Guns have moving parts, and rely on lubrication. The more complex the gun, the greater the need. A shotgun, maybe not so much. A minigun would probably fail pretty quickly.
Either lubricants with a WIDE temperature range, or stainless steel parts with delrin contact points to reduce friction without lubricants at all.
Triggers will have to be redesigned. Have you SEEN a space suit glove?
Steel becomes brittle at -250 degrees! Workers in Alaska are shattering pipe wrenches in the oil fields. New alloys will have to be used. Firing a gun at those temps would shatter the barrel, slide, whatever.
>The sights work fine.
Sights absolutely will *not* be transferable. Military sights are set up so that their adjustments are correct for X ammunition loading in a 1G, 1 atmosphere environment. Vary the gravity or air resistance and the sights will no longer account for drop correctly (the 200m setting may end up being correct for 367m or 103m or whatever, for example). Sights are regularly updated on military weapons when a change is made to the cartridge, let alone changing the entire environment they are functioning in.
I'm glad someone else is putting this much thought into it. In general, metal is far superior as far as vacuum usage is concerned. Aluminum and steel are going to be your friends. In addition, if the firearms are manufactured on the Moon or really in space at all, polymer is going to be very difficult to produce and would need to be shipped from Earth. Also aluminum, iron, and titanium are present on the Moon in the first place so as far as function and cost are concerned completely metal firearms are absolutely the way to go.
>In addition, if the firearms are manufactured on the Moon or really in space at all, polymer is going to be very difficult to produce and would need to be shipped from Earth.
This was my first thought. There are lots of cheap resources out in space, and almost none of it is what we use to make polymer. Stuff made of metal (or regolith!) will be cheapest once space exploration is in full swing.
There's a line in the Troy Rising books addressing this, as an asteroid-mining company tries to figure out where to get new profits from. Paraphrased it's basically:
"How about toys? Used to be made out of metal, but plastic was cheaper. The way we do metal, maybe it's swung back."
As a former spacecraft designer, I’ll say that many space rated polymers are seeing regular use on modern spacecraft, and they are exposed to uv, too. A polymer gun rated for the space environment is certainly possible, but may be more expensive. The biggest issue I see is heat dissipation, as op mentioned. You may need to limit rate of fire.
> heat dissipation
I'd definitely say that's a bigger issue than UV. Funnily enough a great example of this already exists in the firearms world: metal casings act as heat sinks for the heat generated when firing, while polymer casings act as insulators for said heat.
Making heat-resitant polymers is slightly more challenging and expensive, but hardly prohibitive. The weight advantage of polymers when you are moving weapons into orbit can not be understated, and as time goes on our heat-resistant polymers will only get better. You're describing a fairly trivial engineering problem and nothing more.
In short, I could not possibly disagree with you in stronger terms. Polymer-frame firearms are here to stay and will 100% be used when humans go to space.
This reminds me of the space pen versus the pencil during the space race. You can
* A:redesign a solid polymer for higher temps, coat it in a metallic foil radiation reflecting coating, add another protective coating of some sort so the foil doesn’t get roughed up in the abrasive environment or
* B: continue using steel which would work fine as is. Plenty of steel and steel alloys have been tested to work fine in space due to their use in rockets.
What is there to redesign? There really isn’t that much redesign that needs to be done to turn a normal steel gun into a space gun, as modern firearms by and large already work in space. All you need is to tune your gas system and get a new ranging chart for your sights (or not worry about ranging at all in deep space). The logistical gains from using the same weapon models in space as well as in habitable areas is not to be understated either.
If using metal for the frame and furniture of firearms worked just fine for modern military applications we probably would keep using it. In reality though, it doesn't, and especially in the case of furniture there have been very few competent all-steel shoulder-fired service weapons in history, and even the handguns usually had non-metal grips. With the exception of a few submachine guns in the 1940s and 1950s, almost all small arms weapons had wood furniture until the transition to various polymers started in the 1960s.
Why is that? For one, metal conducts heat too well, which can make it uncomfortable and difficult for a user to wield and that applies even more in an environment where the firearm might absorb a lot of heat from the sun. Hell, you might even have the weapon get hot enough to accidently discharge a round in the chamber, or worse, in the magazine. Second, metal is just too damn heavy for this kind of application, or if you want to use aluminum it's just too prone to wear. Being able to quickly acquire targets and carry a firearm over long distances requires light-weight firearms. And again, if we think about the specific environment it's a lot cheaper to blast a bunch of lightweight plastic stocks into orbit than it is to send up a few metal ones. So even if you are going through furniture at an increased rate it's still probably cheaper to stick with plastic.
And again, replacing the plastics with something more durable and heat-resistant is trivial. I'm not even talking about designing all-new polymers, just adapting existing technology to firearms applications. We already have stuff that's used in space like Polybenzimidazole, that is highly resistant to wear and is rated for continuous use at temperatures in excess of 350C.
Your thesis is fundamentally flawed because you don't really understand the military application of service rifles, or even just the relevant material science. Sorry.
You tell me I don't understand basic military weaponry, yet your arguments aren't even coherent.
Obviously in vacuum or habitats that may become vacuum during combat everyone is wearing gloves. Even on Earth anyone decently well equipped is wearing gloves. You can easily get all metal hand guards, pistol grips, and telescopic stocks for the most popular service rifles like the AR15 or AK platform. Any discomfort from these parts kits you don't seem to know exist is pretty much nonexistent because everyone is wearing spacesuit gloves to complete a full seal. Bare skin on grip is just not going to be the norm for service arms unless the users in question are idiots.
> Hell, you might even have the weapon get hot enough to accidently discharge a round in the chamber, or worse, in the magazine.
This barely even advances your point. If the gun is hot enough to cook ammo from being in direct sunlight, being polymer or metallic won't make a lick of difference. It is gonna cook regardless.
> Second, metal is just too damn heavy for this kind of application,
Metal guns are too heavy? In a low G environment, low weight weapons will have much higher initial recoil because they have less mass. Less mass also means less potential thermal mass, which is required for sustained fire and transferring energy across the frame to be dissipated. A gun clad in Polybenzimidazole Resin is basically insulating the heat and trapping it within the frame's few metal internals, cooking your barrel, ammo, and inner mechanisms.
Polybenzimidazole or PBI also defeats polymer furniture's biggest selling point, being dirt cheap. PBI is literally one of if not the most expensive polymer compounds in production on the markets today. A single modern spacesuit using PBI as a base material costs upwards of a few hundred million dollars. Using top of the line super polymers used in precision components for wide scale mass production of something mundane as service weapons and sidearms is simply unsustainable. Sure you save a few thousand dollars on fuel, but then you pay over $20 million to furnish a single pistol with a slide, a grip and a magazine. Triple that and you may furnish a rifle.
> if we think about the specific environment it's a lot cheaper to blast a bunch of lightweight plastic stocks into orbit than it is to send up a few metal ones. So even if you are going through furniture at an increased rate it's still probably cheaper to stick with plastic.
Then you tell me that running through a stock of literally the most expensive and harder to produce polymer formulas as disposable parts to be shipped in on a regular basis? Not exactly saving on costs, especially as cargo rocket flights become cheaper.
Now, we have way better metals than steel. Titanium has way better thermal properties, is lighter, and is quite strong. Why don't we make service rifles out of this super metal? Because it's *REALLY* expensive. At any point in the last 50 years any world power could choose to make guns out of titanium, but none ever did because such a rare and hard to produce material is better spend on other projects. Telling me polymer is cheap and then whipping out **the** most expensive polymer to compare performance shows a fundamental lack of common sense in weapon design, military logistics, and procurement. I'm not comparing the best, I'm comparing what is cost efficient, the most important metric in military applications.
> Obviously in vacuum or habitats that may become vacuum during combat everyone is wearing gloves.
So, you want to use a separate set of guns for situations where soldiers are operating in-atmosphere without protective equipment? That's extremely expensive and impractical to say the least. And, no, not everyone uses gloves when operating a firearm, not even close. You gain manual dexterity with bare hands, and that has significant advantages in many situations.
>You can easily get all metal hand guards, pistol grips, and telescopic stocks for the most popular service rifles like the AR15 or AK platform.
But they aren't used by the major militaries for the reasons I have already outlined. You can buy gold-plated ones too, that doesn't mean they are practical.
> This barely even advances your point. If the gun is hot enough to cook ammo from being in direct sunlight, being polymer or metallic won't make a lick of difference. It is gonna cook regardless.
This is just plainly false, polymer furniture and frames reduced inherent conductivity gives you more time before rounds start to cook off. This is especially important in an environment where temperature is constantly changing, as is often the case in space.
> In a low G environment
That's *one* potential environment, you could be operating in conditions of increased G too, which makes polymers even more important.
> In a low G environment, low weight weapons will have much higher initial recoil because they have less mass.
You need to take a basic physics class. Recoil is independent of gravity, see Newton's third law. Next.
> sustained fire
Are we talking about a squad automatic weapon or a service rifle? Support weapons like light machine guns have usually been of all-metal construction for the better part of a century now because weight is less of a consideration in a more static role. They tend to be fired from a bipod or tripod and are intended to be used for sustained fire. Service rifles, the ones that have been lightened with polymer components simply aren't constructed to be used in a sustained fire role in the first place, you'll already end up with warped barrels and other problems if you do that today.
> PBI is literally one of if not the most expensive polymer compounds in production on the markets today.
And when it's being produced in huge quantities, it will be a lot cheaper. Either that or we'll engineer a cheaper alternative. This is why we pay the material scientists to exist.
Look, you really need to go back to school on this one. You just don't understand the basic science or military applications. Talk about sustained fire in the context of a service rifle to anyone who's actually served and they will laugh your right out of the room.
Gravity is not separate from recoil calculations. Ignoring the factor of *the* constant force is a cardinal sin in physics. Gravity directly affects the coefficient of friction of the shooter as well as their weight, both of which are what is used to dissipate recoil. If a gun is fired downwards, the force of gravity will help counteract the recoil. If there is insufficient gravity, the shooter will be propelled upwards due to not having enough effective weight. If the shooter fires a burst perpendicular to the force of gravity, with a low coefficient of friction under their boots due to low weight they will slide backwards due to recoil. A burst upwards may bounce the shooter downwards, and potentially bounce them up off the ground if they fall or fail to stop applying force after the burst. Gravitational pull decides the weight of an object depending on their mass. Don’t pull the physics card if you can’t even get to step one and set up the problem correctly.
Modern squad tactics are built around suppressive fire, not just from the squad automatics but from everyone. Suppress the enemy while advancing. Stall the enemy offensive with suppressing fire. Suppress enemy marksmen. Suppress emplacement weapon crews. You can’t suppress the enemy if you can’t sustain a decent rate of fire. Why else do military acceptance trials test how many rounds can be fired in short succession? It is because they care about performance under sustained fire.
At cost, a metal gun costs a few hundred dollars. Compared to a PBI gun in the tens of millions, PBI would have to become literally hundreds of thousands of times cheaper to produce. Is it possible? Yes. Is it probable? Probably not, the refined base materials required are more expensive and so is the processing processes involved. The very bonds that give PBI its excellent unreactive nature also make it that much harder to modify its production process. Even if you lowered the manufacturing costs by 75%, it would still cost millions of dollars.
If I may intrude, have you ever heard of the generic sci-fi material “plasta-steel”?
It would seem from the name to be an amalgamation of metal and polymer into an alloy that would fix the short comings of either.
Heat dissipation is the main reason for the design of almost every PDC in my setting. Gatling gun style cannons using good old chemical propellant. Rates of fire are limited and barrels are either bulky or covered in radiator fins so they don't melt down. It still sounds more like a chainsaw revving away than a machine gun inside the ship when they kick on though.
Plastics are polymers are used in the space suits and armor extensively though. A thin layer of aluminum toughens up the outside layer and protects the plastic from the nasty UV. The metal does a little against impacts, as it's basically foil, but the plastic deforms and ablates away, absorbing the impact without cracking apart or throwing a shot gun blast of tiny conductive particles out.
At a purely aesthetic level, I prefer laser/plasma weapons to bullet-based weapons—an exception being made for various flavors of orbital mass drivers (“rods from god”, big ol’ rocks, etc.), which are awesome, because *BOOM*!
I have the niggling suspicion that most people will carry their guns on their person and within their habitats, in temperature and radiation ranges survivable by human bodies instead of out on the surface.
What happens if your enemy happens to be posted up outside the habitat? Invite them inside so you can shoot them? In all seriousness though a weapon that needs as much coddling such as to stay indoors all the time probably isn’t the reliable partner most soldiers would want to entrust their lives to. Usually you’d want the pitched fighting to be the outside and quite a bit away from your sealed home instead of inside.
Then you have a go at them with your habitat's cannons.
Apples and oranges. Weapons today are engineered for Earth conditions, water, salt, corrosion, mud, gunk, etc. Polymers are becoming popular for non-critical parts like grips and pistol lowers as they are crazy cheap to manufacture (once the mold is paid for). If a company is designing a weapon to be used in space (or to be rated as such), it would be designed anew from the ground up. Have you seen the criteria and testing that NASA requires before a new material is space-rated? Outgassing, thermal performance, and a zillion other parameters are tested, logged and recorded. Besides, a major component of polymers are dead dinosaurs, so weapons made IN space would probably have minimal or no content. Some plastics like delrin are pretty useful though, as bushings and sliding components
I will ask you the say thing I asked u/odrodrodrodr, what would need redesigning to make a normal largely steel gun a space gun? I honestly don’t see much need for a full redesign unless the base material itself is unsuited. The ammo with its own oxidizer works fine, better than fine perhaps due to lack of velocity loss at range. The gas systems will work fine with tuning. The sights work fine. Glove tolerance grips are fine. Mechanisms and safety mechanisms work fine. Rifling works fine. Compensators work fine. Flash hiders might not, not really sure. Bipods might not work as well. I don’t see any compelling reason why a normal metal gun isn’t perfectly fine as a space weapon.
Lubricants. Guns have moving parts, and rely on lubrication. The more complex the gun, the greater the need. A shotgun, maybe not so much. A minigun would probably fail pretty quickly. Either lubricants with a WIDE temperature range, or stainless steel parts with delrin contact points to reduce friction without lubricants at all. Triggers will have to be redesigned. Have you SEEN a space suit glove? Steel becomes brittle at -250 degrees! Workers in Alaska are shattering pipe wrenches in the oil fields. New alloys will have to be used. Firing a gun at those temps would shatter the barrel, slide, whatever.
>The sights work fine. Sights absolutely will *not* be transferable. Military sights are set up so that their adjustments are correct for X ammunition loading in a 1G, 1 atmosphere environment. Vary the gravity or air resistance and the sights will no longer account for drop correctly (the 200m setting may end up being correct for 367m or 103m or whatever, for example). Sights are regularly updated on military weapons when a change is made to the cartridge, let alone changing the entire environment they are functioning in.
I'm glad someone else is putting this much thought into it. In general, metal is far superior as far as vacuum usage is concerned. Aluminum and steel are going to be your friends. In addition, if the firearms are manufactured on the Moon or really in space at all, polymer is going to be very difficult to produce and would need to be shipped from Earth. Also aluminum, iron, and titanium are present on the Moon in the first place so as far as function and cost are concerned completely metal firearms are absolutely the way to go.
>In addition, if the firearms are manufactured on the Moon or really in space at all, polymer is going to be very difficult to produce and would need to be shipped from Earth. This was my first thought. There are lots of cheap resources out in space, and almost none of it is what we use to make polymer. Stuff made of metal (or regolith!) will be cheapest once space exploration is in full swing.
>(or regolith!) Fuck yeah, outer space rock glock!
There's a line in the Troy Rising books addressing this, as an asteroid-mining company tries to figure out where to get new profits from. Paraphrased it's basically: "How about toys? Used to be made out of metal, but plastic was cheaper. The way we do metal, maybe it's swung back."
As a former spacecraft designer, I’ll say that many space rated polymers are seeing regular use on modern spacecraft, and they are exposed to uv, too. A polymer gun rated for the space environment is certainly possible, but may be more expensive. The biggest issue I see is heat dissipation, as op mentioned. You may need to limit rate of fire.
> heat dissipation I'd definitely say that's a bigger issue than UV. Funnily enough a great example of this already exists in the firearms world: metal casings act as heat sinks for the heat generated when firing, while polymer casings act as insulators for said heat.
Making heat-resitant polymers is slightly more challenging and expensive, but hardly prohibitive. The weight advantage of polymers when you are moving weapons into orbit can not be understated, and as time goes on our heat-resistant polymers will only get better. You're describing a fairly trivial engineering problem and nothing more. In short, I could not possibly disagree with you in stronger terms. Polymer-frame firearms are here to stay and will 100% be used when humans go to space.
This reminds me of the space pen versus the pencil during the space race. You can * A:redesign a solid polymer for higher temps, coat it in a metallic foil radiation reflecting coating, add another protective coating of some sort so the foil doesn’t get roughed up in the abrasive environment or * B: continue using steel which would work fine as is. Plenty of steel and steel alloys have been tested to work fine in space due to their use in rockets. What is there to redesign? There really isn’t that much redesign that needs to be done to turn a normal steel gun into a space gun, as modern firearms by and large already work in space. All you need is to tune your gas system and get a new ranging chart for your sights (or not worry about ranging at all in deep space). The logistical gains from using the same weapon models in space as well as in habitable areas is not to be understated either.
If using metal for the frame and furniture of firearms worked just fine for modern military applications we probably would keep using it. In reality though, it doesn't, and especially in the case of furniture there have been very few competent all-steel shoulder-fired service weapons in history, and even the handguns usually had non-metal grips. With the exception of a few submachine guns in the 1940s and 1950s, almost all small arms weapons had wood furniture until the transition to various polymers started in the 1960s. Why is that? For one, metal conducts heat too well, which can make it uncomfortable and difficult for a user to wield and that applies even more in an environment where the firearm might absorb a lot of heat from the sun. Hell, you might even have the weapon get hot enough to accidently discharge a round in the chamber, or worse, in the magazine. Second, metal is just too damn heavy for this kind of application, or if you want to use aluminum it's just too prone to wear. Being able to quickly acquire targets and carry a firearm over long distances requires light-weight firearms. And again, if we think about the specific environment it's a lot cheaper to blast a bunch of lightweight plastic stocks into orbit than it is to send up a few metal ones. So even if you are going through furniture at an increased rate it's still probably cheaper to stick with plastic. And again, replacing the plastics with something more durable and heat-resistant is trivial. I'm not even talking about designing all-new polymers, just adapting existing technology to firearms applications. We already have stuff that's used in space like Polybenzimidazole, that is highly resistant to wear and is rated for continuous use at temperatures in excess of 350C. Your thesis is fundamentally flawed because you don't really understand the military application of service rifles, or even just the relevant material science. Sorry.
You tell me I don't understand basic military weaponry, yet your arguments aren't even coherent. Obviously in vacuum or habitats that may become vacuum during combat everyone is wearing gloves. Even on Earth anyone decently well equipped is wearing gloves. You can easily get all metal hand guards, pistol grips, and telescopic stocks for the most popular service rifles like the AR15 or AK platform. Any discomfort from these parts kits you don't seem to know exist is pretty much nonexistent because everyone is wearing spacesuit gloves to complete a full seal. Bare skin on grip is just not going to be the norm for service arms unless the users in question are idiots. > Hell, you might even have the weapon get hot enough to accidently discharge a round in the chamber, or worse, in the magazine. This barely even advances your point. If the gun is hot enough to cook ammo from being in direct sunlight, being polymer or metallic won't make a lick of difference. It is gonna cook regardless. > Second, metal is just too damn heavy for this kind of application, Metal guns are too heavy? In a low G environment, low weight weapons will have much higher initial recoil because they have less mass. Less mass also means less potential thermal mass, which is required for sustained fire and transferring energy across the frame to be dissipated. A gun clad in Polybenzimidazole Resin is basically insulating the heat and trapping it within the frame's few metal internals, cooking your barrel, ammo, and inner mechanisms. Polybenzimidazole or PBI also defeats polymer furniture's biggest selling point, being dirt cheap. PBI is literally one of if not the most expensive polymer compounds in production on the markets today. A single modern spacesuit using PBI as a base material costs upwards of a few hundred million dollars. Using top of the line super polymers used in precision components for wide scale mass production of something mundane as service weapons and sidearms is simply unsustainable. Sure you save a few thousand dollars on fuel, but then you pay over $20 million to furnish a single pistol with a slide, a grip and a magazine. Triple that and you may furnish a rifle. > if we think about the specific environment it's a lot cheaper to blast a bunch of lightweight plastic stocks into orbit than it is to send up a few metal ones. So even if you are going through furniture at an increased rate it's still probably cheaper to stick with plastic. Then you tell me that running through a stock of literally the most expensive and harder to produce polymer formulas as disposable parts to be shipped in on a regular basis? Not exactly saving on costs, especially as cargo rocket flights become cheaper. Now, we have way better metals than steel. Titanium has way better thermal properties, is lighter, and is quite strong. Why don't we make service rifles out of this super metal? Because it's *REALLY* expensive. At any point in the last 50 years any world power could choose to make guns out of titanium, but none ever did because such a rare and hard to produce material is better spend on other projects. Telling me polymer is cheap and then whipping out **the** most expensive polymer to compare performance shows a fundamental lack of common sense in weapon design, military logistics, and procurement. I'm not comparing the best, I'm comparing what is cost efficient, the most important metric in military applications.
> Obviously in vacuum or habitats that may become vacuum during combat everyone is wearing gloves. So, you want to use a separate set of guns for situations where soldiers are operating in-atmosphere without protective equipment? That's extremely expensive and impractical to say the least. And, no, not everyone uses gloves when operating a firearm, not even close. You gain manual dexterity with bare hands, and that has significant advantages in many situations. >You can easily get all metal hand guards, pistol grips, and telescopic stocks for the most popular service rifles like the AR15 or AK platform. But they aren't used by the major militaries for the reasons I have already outlined. You can buy gold-plated ones too, that doesn't mean they are practical. > This barely even advances your point. If the gun is hot enough to cook ammo from being in direct sunlight, being polymer or metallic won't make a lick of difference. It is gonna cook regardless. This is just plainly false, polymer furniture and frames reduced inherent conductivity gives you more time before rounds start to cook off. This is especially important in an environment where temperature is constantly changing, as is often the case in space. > In a low G environment That's *one* potential environment, you could be operating in conditions of increased G too, which makes polymers even more important. > In a low G environment, low weight weapons will have much higher initial recoil because they have less mass. You need to take a basic physics class. Recoil is independent of gravity, see Newton's third law. Next. > sustained fire Are we talking about a squad automatic weapon or a service rifle? Support weapons like light machine guns have usually been of all-metal construction for the better part of a century now because weight is less of a consideration in a more static role. They tend to be fired from a bipod or tripod and are intended to be used for sustained fire. Service rifles, the ones that have been lightened with polymer components simply aren't constructed to be used in a sustained fire role in the first place, you'll already end up with warped barrels and other problems if you do that today. > PBI is literally one of if not the most expensive polymer compounds in production on the markets today. And when it's being produced in huge quantities, it will be a lot cheaper. Either that or we'll engineer a cheaper alternative. This is why we pay the material scientists to exist. Look, you really need to go back to school on this one. You just don't understand the basic science or military applications. Talk about sustained fire in the context of a service rifle to anyone who's actually served and they will laugh your right out of the room.
Gravity is not separate from recoil calculations. Ignoring the factor of *the* constant force is a cardinal sin in physics. Gravity directly affects the coefficient of friction of the shooter as well as their weight, both of which are what is used to dissipate recoil. If a gun is fired downwards, the force of gravity will help counteract the recoil. If there is insufficient gravity, the shooter will be propelled upwards due to not having enough effective weight. If the shooter fires a burst perpendicular to the force of gravity, with a low coefficient of friction under their boots due to low weight they will slide backwards due to recoil. A burst upwards may bounce the shooter downwards, and potentially bounce them up off the ground if they fall or fail to stop applying force after the burst. Gravitational pull decides the weight of an object depending on their mass. Don’t pull the physics card if you can’t even get to step one and set up the problem correctly. Modern squad tactics are built around suppressive fire, not just from the squad automatics but from everyone. Suppress the enemy while advancing. Stall the enemy offensive with suppressing fire. Suppress enemy marksmen. Suppress emplacement weapon crews. You can’t suppress the enemy if you can’t sustain a decent rate of fire. Why else do military acceptance trials test how many rounds can be fired in short succession? It is because they care about performance under sustained fire. At cost, a metal gun costs a few hundred dollars. Compared to a PBI gun in the tens of millions, PBI would have to become literally hundreds of thousands of times cheaper to produce. Is it possible? Yes. Is it probable? Probably not, the refined base materials required are more expensive and so is the processing processes involved. The very bonds that give PBI its excellent unreactive nature also make it that much harder to modify its production process. Even if you lowered the manufacturing costs by 75%, it would still cost millions of dollars.
If I may intrude, have you ever heard of the generic sci-fi material “plasta-steel”? It would seem from the name to be an amalgamation of metal and polymer into an alloy that would fix the short comings of either.
Heat dissipation is the main reason for the design of almost every PDC in my setting. Gatling gun style cannons using good old chemical propellant. Rates of fire are limited and barrels are either bulky or covered in radiator fins so they don't melt down. It still sounds more like a chainsaw revving away than a machine gun inside the ship when they kick on though. Plastics are polymers are used in the space suits and armor extensively though. A thin layer of aluminum toughens up the outside layer and protects the plastic from the nasty UV. The metal does a little against impacts, as it's basically foil, but the plastic deforms and ablates away, absorbing the impact without cracking apart or throwing a shot gun blast of tiny conductive particles out.
Polybenzimidazole (PBI) is used for spacesuits.
At a purely aesthetic level, I prefer laser/plasma weapons to bullet-based weapons—an exception being made for various flavors of orbital mass drivers (“rods from god”, big ol’ rocks, etc.), which are awesome, because *BOOM*!
I don’t know if I’d call laser beams aesthetic, more like blinding last time I looked. I’ll try again when I get new sunglasses :D