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I'm working on a setting for an rpg and I definitely want to go for a distant future, post-apocalyptic world, not unlike Numenera. In Numenera guns of all different kinds would be considered Cyphers or Artifacts, so either limited in use or uncommmon. What would be some feasible ways to incorporate more readily available firearms and ammunition into a far-future? One idea was having some kind of solar or ambient charging railguns that could fire any object small enough to fit in the barrel. My hesitation is what would such rechargeable batteries have on the setting as a whole? I definitely want to make travelling notably faster than horse-like animals a rarer possibility.

I'm ok with needing some scavenging, but I don't want my players to be forced to leave weapons behind due to ammunition scarcity or incompatibility.

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closed as too broad by sphennings, JBH, L.Dutch, John, Slarty Nov 25 '17 at 23:24

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.

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    $\begingroup$ Welcome to WB:SE. There are amazingly creative people here, but they need a narrow enough scope to provide you with a good answer. This question is very broad and it's not entirely clear exactly what you're asking. Remember that if you're just fishing for ideas, that's generally off-topic because it can't be specifically answered. You might consider reviewing this post for help with asking great questions. Thanks! $\endgroup$ – JBH Nov 24 '17 at 21:30
  • $\begingroup$ Guns are relatively simple mechanical construct and should easily be reinvented even if modern civilization collapsed. $\endgroup$ – A. C. A. C. Nov 24 '17 at 21:34
  • $\begingroup$ @A.C.A.C., I think by "guns" do you're specifically talking about slug throwers. Rail guns wouldn't be simple and directed energy weapons (OP says distant future but doesn't qualify what that means) would be very diffcult to reinvent. Was that what you were going for? $\endgroup$ – JBH Nov 24 '17 at 21:38
  • $\begingroup$ @JBH By gun, I mean a projectile weapon of any sort where you pull a trigger and a projectile files at high speeds to cause damage. $\endgroup$ – A. C. A. C. Nov 24 '17 at 22:12
  • $\begingroup$ Any punk gang banger with a piece of pipe and clothes pins can assemble a "zip gun". Gunpowder and ammunition requires only 17th century tech for mass production. $\endgroup$ – pojo-guy Nov 25 '17 at 16:00
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I've often imagined the post-apocalypse to fall in love with ... potato cannons.

The design simply requires harder pipes (PVC, steel, wood), some softer, yet incompressible material to act as the bullet (potato, chickpeas, play-doh, meat, you-name-it), and the pressure-generating mechanism. The latter can be:

  • simply pumping air in a reservoir using a bicycle pump. Fill a reservoir, and open a valve, or just use the power of your arms to eject the slug, like a cheap water pump.

  • using propane gas (or other flammable gases), or alcool, or acetylene, or generic propellant: fill a tank, close the tank and light a spark and let the combustion gas eject the slug at high velocity, as is the case for low-budget potato cannons

The linked wikipedia page has a list of designs that is far more exhaustive than what I can add. Common theme to many of these designs is that they can be built from materials that should be easy to scavenge from the ruins of a dead civilization, and very easy to run and maintain. The resulting weapons may not be as accurate, efficient and overall deadly as modern guns, but that did not seem to be a crucial issue.

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  • $\begingroup$ Simple potato gun has small chamber pressure and laughable projectile energy. To get anything useful you need quite complex design with pressurizing of the mix before ignition or smthg else. And even then you have small energy that is easy to counter with simplest armor. If there are pipes lying around then there are steel sheets as well. Though I guess bulletproof armor can be useful plot device for a good rpg master. $\endgroup$ – Vashu Nov 25 '17 at 10:34
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    $\begingroup$ When we had a gun registry in Canada, you nominally had to register anything that would send a projectile faster than 500 feet per second. One guy succeeded in getting this with potato gun. I think he used acetylene as his propellant. 500 ft/s gives you a non-air resistance range of 2.6 km or about a mile and a half. $\endgroup$ – Sherwood Botsford Nov 25 '17 at 15:08
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I suppose your question can be reformulated - "How single craftsman would make firearm if he had some knowledge from high level civilization"

The most primitive weapon wold be hand forged smooth-bore mzzleloaded hangonne.

enter image description here

Here you can see how a gun like this was made. It would be short and heavy, but more powerful and cheaper than an arbalet. Some artisans would make lighter and longer weapons, think musket proportions, they would be much more expensive.

Grained black powder based on potassium nitrate wold be used(actual handgonnes used sodium nitrate which is too hydroscopic). But I would expect a lot of gunpowder based on potassium chlorate, made by electrolysis. It is more quick-burning so it is worse for guns, but it would be cheaper and it would allow to produce primers with most primitive tools(fans of 1632 series made primers like this).

So flinlocks or anything more primitive would be rare - primers are quite easy to make and they are very convenient.

Round lead balls would be used rarely as well. Expansive bullets are easy to make and they are much more accurate. This is how expansive bullet for smoothbore looks like - Nessler ball.

enter image description here

And I am pretty sure you are familiar with it's counterpart for rifles - Minie ball.

Many of those firearms wold have rifling as well, it was often made by craftsman with machine like this.

enter image description here

With Minie bullet rifled mzzleloader is as fast as smoothbore so rifled weapons wold be much more common.

And finally there would be some breechloaders and primitive cartridges around, made from wound brass sheet.

enter image description here

Anything more complex is out of rich of a simple craftsman with primitive tools. As for

// ammunition scarcity or incompatibility

I am afraid you will have a lot of incompatibility with hand made weapons. Most likely for muzzleloaders everybody would make their own ammo.

enter image description here

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It would probably be much easier to revert to simpler technology. Crossbows logbows and blowpipes could easily be provide with ammunition for a long time compared to fire arms. Unless the firearms were of a good quality that provided rapid fire, good range and lots of ammon they could easily be overwelmed by simpler technology.

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You have some issues to address: If your tech is limited to travel <= horse, then gunpowder and a few variants are your best bet. Batteries of reasonable power density are non-trival to make, as are solar cells. Neither last forever. Current Li-Ion batteries are good for about 500 cycles. Solar cells typically degrade about 20% over the 25 year projected life. Not clear if not using them extends their life.

A rail gun is also non trivial and depends on the electrical properties of the projectile. You will get different results between a nail and a screw. You could get around this by using non-conductive ammo and a shuttle in the rail gun. The shuttle is stopped and reused. Railguns generally use really large capacitors instead of batteries to get the currents necessary.

A square foot of 20% efficient solar cell can generate about 16W when supported at right angles to the sun near noon on a clear day. A kW of solar cell generates from 800 kWh (Germany -- rainy climate) to 1400 kWh (American Southwest) of energy per year.

A .303 has about 2400 ft-lbs energy. Converting to joules you get about 3300 J or not quite 1 watt hour. So if you had a way to efficiently turn battery energy into projectile energy it would be reasonable to carry. Your solar cell would store about 16 rounds per hour. Call it 10 to allow for inefficiencies.

Note that sending a heavier projectile at a lower speed delivers the same momentum (impact) with lower energy requirements.

In a watermill, 1800 level tech world, it may be reasonable to make the equivalent of a civil war mini-ball rifle. This still requires 'factories' (A place where a bunch of people work at various stages of production.) You still need decent steel produced in significant quantities. You won't make rifle barrels out of salvaged rebar.

Give consideration to non-firearms.

Bow & Arrow. Takes a long time to learn, and needs practice to keep up. You need to be quite fit to fire off 12 arrows a minute with a 100 lb bow. Bows are sensitive to moisture, and arrows are time consuming to make. https://en.wikipedia.org/wiki/Archery

Crossbow. Easier to learn. Slower in use. Bolts are less fussy to make. https://en.wikipedia.org/wiki/Crossbow

Atlatl. In effect an extension of the arm, used to hurl what amounts to a large arrow or a small spear. Because of the large motion involved, it is not a sneaky weapon. https://en.wikipedia.org/wiki/Spear-thrower

Sling. This is another one that takes a fair amount of practice to get good. However a sling is the lightest weapon in this list, and the ammunition (stones) is common. In particular the staff sling has advantages in a general battle. Slings are less subject to damage from moisture compared to bows.

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