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Apologies in advance, this is going to be a bit of a long read.

I am working through the process of fleshing out a science fiction world and want to establish the limits of technology fairly early on, one of these technologies is weaponry and I'm having a hard time deciding on the function and extent of man portable firepower, which is fairly important to the story.

Lets establish a few things humanity has already accomplished, to give you an understanding of the technical level achieved.

Several moons and planets have already been settled and terraformed, with terraforming equipment being able to improve habitability by up to 50% its original state.

FTL travel is possible, but limited to certain lanes that open and close depending on the orientation of solar systems as the universe rotates on its axis.

Ground vehicles have by in large abandoned wheels, instead they use repulsor tech to keep the vehicle suspended off the ground by about 20 inches. This technology is highly efficient, and stays on even when the vehicle is not running, however the vehicle is lowered to about two inches off the ground to conserve power. Given extended periods without use, the system would eventually run out of power and need to be jumped. These ground vehicles range from small single-seat craft to vehicles the size of a semi-truck, but are exceedingly cheap. One the size of a family sedan would only cost about as much as a consumer motorbike.

Aircraft have risen substantially in popularity, and use a combination of modern flight principles, and the repulsor tech mentioned above that makes the amount of training and skill required to fly these craft substantially lower, and the safety has also been massively improved. In-Atmosphere shuttles are owned by most upper middle class families, and are heavily used in planetary public transit and business. Specialized lanes have been implemented to keep air travel organized.

Economical commercial spaceflight and public transit has been achieved, and costs about twice your average plane ticket to jump between planets, and about five times your average plane ticket for FTL travel to other solar systems. Costs for private citizens to own personal space capable craft is similar to modern day luxury yacht pricing.

Effective particle based shielding to protect against radiation on all space capable craft has been achieved, and this shielding is also moderately effective at stopping microscopic debris moving at very high speeds.

Combat grade shielding has only been around for about for about 15 years, and are much to expensive for any private citizen to afford. Despite this, large corporations and military's have seen large adoption of these shields. These shields are restricted to spacecraft, large aircraft, and large armored groundcraft. They require continuous power and lots of it. They function by suspending a mesh of high energy particles around the craft using strong magnetic fields. These mesh's react similarly to a Non-Newtonian fluid, and are capable of stopping almost all but the largest purely kinetic projectiles. However each impact scatters particles from the shield in large quantities, and the shield will have to move particles from around the shield to fill in the missing portions, causing it to lose density. When a shield becomes so thin that it is no longer effective, the generator will shut down.

The first energy based arms are coming onto the market to counter this, and exists as a hybrid kinetic/energy explosive shell. This technology works on very similar principals to shields themselves. Large shells fired from mounted turrets or cannons contain their own small energy field generators in the rear of the projectile. These generators are activated by the rapid rotation applied when fired from a rifled barrel, and sheath the projectile in a swath of high energy particles. These energy sheaths react much more strongly with combat shields, and can penetrate much quicker than standard projectiles. Usually shells that penetrate will still have their energy sheaths ripped off by the shields.

These shells exist at their largest in 800mm, and smallest at 30mm. There are single shot recoilless rifles, similar to a Carl Gustav, fielded by infantry that fire these shells for anti-tank purposes, and there are single shot 30mm rifles that are capable of penetrating the shields of combat shuttles and are designed to damage engine components/kill the crew. However at this time all other man portable firearms are still purely kinetic.

This is where you lovely folk come in. With this general level of technology, how would you envision standard arms like rifles, handguns, and scatterguns? My only wish is the the firearm itself should be as close to purely mechanical as possible. Modern weapons get all the energy they need to function by burning gunpowder, meaning that you never have to plug in your rifle to recharge, and if you have a dud round you simply chamber a new cartridge and your ready to rock and roll. I can't personally see people abandoning the reliability of this system. So whatever propellant, or energy you devise must contain all of the power to deliver the projection and work the action.

The actual story being told in this universe will take place on one of the most distant colonies from the Sol System, so reliability and ability to manufacture more ammunition and arms without support from Earth is crucial.

You can create your own elements/minerals/compounds that have any characteristics you want. If you want to use electronic tech such as railguns, make a compelling case that the electronics in the rifle would be highly durable and easy to repair while still keeping all of the energy in the ammunition cartridge itself. I hope you guys can come up with some ideas, because I'm having a hard time myself.

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closed as too broad by John, Alex2006, Starfish Prime, Nosajimiki, Renan Jun 12 at 20:36

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Are you looking for weapons of war or are you looking for hunting rifles? $\endgroup$ – Halfthawed Jun 12 at 18:23
  • $\begingroup$ I would say both. The principals of modern ammunition apply unilaterally, if you decide that you want to distinguish between the two and create different systems for both feel free to. $\endgroup$ – Eric_W Jun 12 at 18:28
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    $\begingroup$ This is asking us to brainstorm for you which is considered unacceptable. All firearms is also very broad. Try asking what current interests and goals for future development in military small arms, with an explanation of why you want said information.. This will give you what you likely want without being closed. $\endgroup$ – John Jun 12 at 18:35
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A frame challenge here - I do not think that integral cartridges with the projectile and the propellant in the same case are actually the most optimal solution from the military point of view. First, contemporary cartridges are quite heavy. Second, there is no interchangeability between the firearms of different caliber. From the point of view of the overall logistics, it would be simpler if all personal weapons used the same type of power cell, even if you would need to supply the projectiles separately - and that is assuming broadly similar energy density (or, rather, specific energy, since we need energy per unit of mass).

Here I will come to my next point. The specific energy of firearm propellants is hard to find on the net - I've found the figures like 4.62 MJ/kg (on the forum here https://www.thehighroad.org/index.php?threads/quick-sciency-question.256262/, which can barely count as the scientific source, I know. But the figure is pretty near to the specific energy of TNT and other explosives to be believable). The energy density of contemporary batteries is about ten times lower then that, but the potential future batteries, like lithium-air, can have specific energy over 6 MJ/kg. If your people have repulsor vehicles, they need even more effective batteries than that. Even with 6 MJ/kg batteries railguns would become on par with firearms as far as the propellant weight is concerned (if my rough calculations are correct - the effectiveness coefficient of firearms is about 30%, while for contemporary experimental railguns and coilguns it's nearer to 20%). And that is counting pure propellant weight, without brass casing.

Next we come to the question of caliber and muzzle energy. If we do not introduce any active recoil suppression technologies, then you are not actually able to improve much over the existing firearms - because of the recoil. It's a limitation of a human body, not of the firearm technology. The repulsor technology you mention though, quite naturally can presume active recoil suppression - and then you can go with higher calibers and muzzle speeds. And it would make more sense to power the recoil suppression by the same battery that powers your railgun than to have a firearm with a separate electric-fed recoil suppression.

So, in conclusion I would argue that technologies you describe would quite naturally lead to personal railguns with recoil suppression, with weight similar to contemporary assault rifles, and bullet weight and muzzle speed similar to heavier sniper rifles. If your want more 'solid' weaponry, civilian hunting weapons and more archaic military weapons could be caseless with ballistics similar to modern firearms - but with lighter cartridges due to the lack of the brass case.

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  • $\begingroup$ You made your case well! I really appreciate effort you put into this answer. I think I will incorporate your idea of railguns with active recoil suppression into the universe, but I think I will have the authorities restrict them to military personnel, as these rifles are getting very close to being able to sling the 30mm hybrid cartridges I envisioned... Seriously well written reply dude! $\endgroup$ – Eric_W Jun 12 at 20:45
  • $\begingroup$ @Eric_W glad to be of help. Your 30mm rifles can certainly use that technology. Although I've envisioned a lighter, shorter anti-personnel weapon. Something in the dimensions of a modern PDW, but with the ballistics of .338 Lapua Magnum seems to me to be reasonable for a railgun with a sufficiently dense battery. $\endgroup$ – Cumehtar Jun 12 at 21:12
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You have built a fine world: a low tech distant province in a world where high tech exists.

The actual story being told in this universe will take place on one of the most distant colonies from the Sol System

I can't personally see people abandoning the reliability of this system

Out in the provinces, they will use old tech that they are comfortable maintaining and repairing, and which can be manufactured locally. If the natives of the planet are fighting wars with each other they might be supplied by their sponsors with some pieces of advanced tech such as you describe, and use 1930s era tech for most of what they do.

A cool thing for your story would be to hybridize. Maybe your hero buys a salvaged wreck and finds some of those 30mm energy shells in it, and realizes he can shoot them from his Kentucky longrifle. Maybe your local tech whiz uses repulsor tech to trick out a trebuchet. Having it all be fancy schmancy is a lot at once, but having your characters be mostly low tech makes more awesome the occasional piece of fancy tech.

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  • $\begingroup$ Thanks dude! I admit, I was inspired by a video game called Rimworld, so I cant take all the credit for the idea, but I think a setting like this has great potential to tell a great story! There will definitely be a wide mix of technology, and I like the way you think with the hybridization! $\endgroup$ – Eric_W Jun 12 at 20:50
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In terms of reliability of firearms over long journeys in the past, nothing comes to mind like the air guns used on the expedition of Lewis and Clark. The way the guns were made required the user to only provide the ammunition, which was a 20 round gravity fed magazine, also extremely ahead of its time (first repeating rifle). The ammo was relatively light, and because it's all you would need to carry, you could bring a lot of it with you.

I could see a variation of this type of rifle used on distant planets, because if there is an atmosphere, you can pressurize it into a tank.

For its specific features, I looked at where the Girandoni failed, and improved it.

When you are working out the aesthetics, consider simplicity and utilitarianism in your design. Likely no HUD would exist, but perhaps a gauge on the tank and a clear portion of the magazine so the user could see their remaining levels. For the magazine, gravity fed systems require the least amount of parts and maintenance, so that likely what these rifles would use.

Tank

The original tank would allow 30 shots, but require 1500 hand pumps to fill, and was extremely fragile. This could be fixed by having an on gun air pump which in the future might be able to instantaneously fill. It could also be made with some polycarbonite space metal blend that weighs less then the stored air, while providing a basically bullet proof tank. The development of these tanks would not be difficult, and the manufacturing of them would be an extreme last resort, as they would almost never fail. (Also the lack of an explosive (gunpowder) would allow this rifle to have a high level of safety in space craft)

Ammo

The original ammo was just lead balls, but this could be modified to what ever elements were available on the planet. You would just have to set one of your mining robots to drill out what ever mm sphere you want, out of whatever material you want, and grow your stock pile. Variations on the ammo for tech-wiz kids would be easy (bomb shots, bird-shot, plasma pulse bomb, etc), the sphere would just have to fit into the Magazine. I imagine that the ideal ammo would be small, air soft like pellets, because they would allow for a massive spread at a high rate of fire. The small size allows for greater projectile speed (I think) allowing for the penetration of skin, muscle, clothing and light armor but without the worry of breaking through the hull of any craft or structure. You would have to hit someone multiple times for a kill, but if they are in a space suit this is all you need.

Having larger ammo and simple mortar tubes that could be used to launch high tech shells on standby would be smart (for Anti Aircraft or Hover Tank situations) and be relatively cheap to develop if the technology for smaller arms I described already exists.

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    $\begingroup$ Yeah, a weapon like this would almost seem ideal for colonists that would have to rely on themselves for most things! I fully admit I didn't really consider air pressure! Thanks for the detailed reply my man, I like that material you invented too, could have multiple uses! $\endgroup$ – Eric_W Jun 12 at 20:56

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