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The situation is the usual, we have lots of junk metal lying around in cities, great but not impossible difficulties with logistics (meaning that a few railroads are in operation at immense cost, but operating nonetheless, and likewise for small naval vessels) and great difficulties with making the right tools to make the right tools and so on. I assume steelmaking would not be an issue at this point for larger societies/groups (you could start a cottage industry with wood gasification, if necessary, and coal hasn't disappeared anywhere, it's just harder to reach).

However, assuming we don't have petroleum-based gun oils (practically no oil-production is happening or left anywhere, and main fuels are food and coal), or access to gunpowder, how could they maintain their weapons? Could a small group of let's say 100-200 people (or similar scale) - given the right circumstances - produce their own reliable firearms or basic artillery, such as grenade launchers given the above circumstances?

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    $\begingroup$ One question per question, please. $\endgroup$ – Mołot Feb 10 '18 at 15:20
  • $\begingroup$ What kind of weapons you have in mind? Do you want them making assault rifle or muskets? $\endgroup$ – Sasha Feb 10 '18 at 17:32
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    $\begingroup$ Firearms made in the last hundred years do not use actual gunpowder. (The American War of Secession was the last major war of the gunpowder age.) And I cannot imagine a future society not being able to make gunpowder -- it's not at all hard to make, and the ingredients can be found just about anywhere. A team of a hundred men can make primitive guns, provided they don't have to grow their own food, make their own clothers, mine their own copper and tin, and in general they can concentrate on making gunpowder, cannons and cannon balls. $\endgroup$ – AlexP Feb 10 '18 at 18:52
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I actually build home made firearms as a hobby. I built one recently in my garage modeled after the ones WW2 resistance members built in basements and garages. It was a a semi-auto version of the STEN gun mentioned in a prior comment. it was actually very simple to build, it actually would have been simpler to make it a machine-gun but that's not legal. It took me about 18 hours over a 2 day period utilizing hand files, a dremmel tool, and some drills and metal saws. I welded mine together but in a post apocalyptic society you could just as easily use rivets in the absence of a welder.

Gun oil can be anything slippery, animal fats or vegetable oils would work fine, some guns (like the STEN I built) need very very little lubrication at all and seem to "prefer" dry operation.

Gunpowder is actually pretty easily made, you just need nitrates, charcoal, and sulfur. They used to produce nitrates in the colonial era by piling animal dung and compost into gravel beds for several months at a time and having lots of people urinate on the whole mess frequently. After several months they would dig up the gravel, wash the tiny nitrate crystals from it, and boil it down for purification. Nitrate crystals also built up naturally in bat caves, saltpeter contains nitrates and can be scraped from cave walls too. all these methods were used regularly in the colonial era, after gathering or producing the nitrates it would then be combined with the aforementioned materials to produce black powder. Keep in mind black powder fouls very quickly and so semi-automatic weapons or machine guns made to use it as a propellant will seize up in pretty short order.

also here's a link to an improvised firearms blog cataloging the sorts of guns various criminals and terrorists have cobbled together. https://homemadeguns.wordpress.com/

heres a link to a few "DIY" machinegun schematics (dont attempt to make any, these are for educational purposes only)

http://www.thehomegunsmith.com/pdf/9mmPistol.pdf

https://www.scribd.com/doc/56030331/Expedient-Homemade-Firearms-BSP-9mm-SMG-P-a-Luty

and last but not least, here is a complete index of several hundred guns you could theoretically build using low tech means: http://www.armchairpatriot.com/Home%20Defense/Construction%20and%20Blueprints/

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    $\begingroup$ Making your own Sten is impressive! What did you do for the barrel? $\endgroup$ – Schwern Feb 11 '18 at 2:54
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    $\begingroup$ My friend is a long time professional gunsmith and so he and I used his equipment to manufacture my own barrel from scratch. Making gun barrels isn't difficult, finding the equipment to do so it the hard part since its specialized enough most machine shops don't have one and the only people selling such machinery demand huge prices because its usually custom made to order. I ought to add that in a post-apocalyptic situation barrels will likely be smooth bore and quite inaccurate unless there are some people in possession of the highly specialized equipment to rifle barrels. $\endgroup$ – TCAT117 Feb 11 '18 at 3:04
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While a lot of the below handwaves over a lot of time they'd need to spend learning by experimentation and failure, if they have the patience, know-how, free-time, and resources to smelt steel (or even melt salvage) they can figure out firearms. They can do black powder bolt-action rifles and revolvers for sure. If they've reached late-19th century tech they can do modern-ish smokeless powder in submachine guns and assault rifles.

First a little bit about "gunpowder".

Black Powder

"Gunpowder" is technically "black powder", a combination of sulfur, charcoal, and potassium nitrate. It detonates relatively slowly requiring long barrels to build up speed, produces a lot of smoke, and leaves a sooty residue that builds up and fouls the weapon.

If they can figure out steel, they can figure out black powder. It's fairly easy to make, and has been made for 1000 years. Sulfur and charcoal are easy to get. Potassium nitrate requires a bit of chemical know how, but not much.

With black powder you can have revolvers, shotguns, rifles, and artillery. You can have simple repeating firearms, bolt-action or lever-action rifles. These don't require any special materials or high quality springs, something surprisingly difficult to make. Since black powder is so low pressure, they don't even require steel, they can be made of iron or brass. Besides, anything more sophisticated will get fouled with black powder residue and fail. No machine guns. No semi-automatic pistols like a Colt-45. No self-loading rifles like an M1 Garand.

You can have normal metallic cartridges, making brass casings is easier than making steel and they can be reused. You can have detachable magazines or stripper clips. However black powder bullets will be slower, and so less accurate and shorter ranged. The lower velocity means bullets need to be heavier to have the same impact. Instead of .30 caliber, you'd be firing .45 or .50 caliber like .45-70 Government.

Smoothbore barrels are easy, anyone with a lathe can bore out a polished steel tube. Rifled barrels require some know-how but are not hard, they've been around since the 15th century, but the quality and accuracy will vary wildly.

You might wind up with something like the 1903 Air Service rifle. A bolt action rifle firing metallic cartridges with a detachable box magazine. Except in black powder, so the barrel would be longer, and firing larger caliber bullets like .45-70 Government. And the parts will be of a lower quality. Watch how Karl of InrangeTV smacks around the bolt of a Mosin-Nagant, it'll be like that but worse.

enter image description here

You can have explosives, but not high explosives. "High" meaning "high velocity" meaning the detonation velocity exceededs the speed of sound creating a shockwave. Black powder explosives are good for clearing stumps, less good as an anti-personnel weapon.

Smokeless Powder

What everyone thinks of as "gunpowder" used in modern firearms is actually "smokeless powder", one of various different compounds that detonate at a high velocity and leave little smoke nor residue. This allows for shorter barrels and more complex mechanisms.

The first really successful smokeless powder was nitrocellulose or "guncutton" in the mid-19th century. This is nitric acid and wood fiber. Easy to make by anyone with some chemical know how. Quality will vary while they gain experience, and there are various improvements to be made.

Having smokeless powder opens up the whole range of modern firearms. The higher detonation velocity means shorter barrels, smaller calibers, higher velocities, longer ranges. The lack of residue means automatic firearms are now possible.

Oddly enough, some modern firearms are easier to make then old time ones. Many modern firearms have simplified construction requiring mostly stamped sheet-metal and very little careful work. You do need good spring steel for springs. Submachine guns are particularly simple, you can be cranking out Sten guns. These were so simple, the were made by resistance forces in occupied Europe. Here's examples made by the Poles in the Warsaw Ghetto.

enter image description here

Later you can make milled AK-style assault rifles, and later cheaper stamped assault rifles. Milling is expensive and requires special tools. Stamping is cheap, but gaining the expertise necessary to do it well enough for an automatic rifle is more difficult than milling as was experienced in the development of the AK-47.

Other simplified emergency and "last ditch" designs from WWII like the Gerat 06 would be possible. Quality will be an issue, and expect many jams while your gunsmiths gain experience.

Smokeless powder also leads to nitroglycerin, the high explosive content of dynamite. High explosive means more effective artillery and grenades.

Lubricants and Solvents

"Gun oil" is not necessary to fire a gun, but it is very helpful to prevent corrosion and wear from metal parts rubbing. Most of it is mineral oil (petroleum based) but vegetable oils work fine, too. The important thing that it's well refined, not break down at high temperatures, nor gum up at low temperatures. The lower the quality the more often you'll have to clean it off and reapply.

Solvents for cleaning are much simpler. Alcohol will do and that's very easy to make. Again, it's the level of refinement that matters.

Rifled Barrels

These are a problem. Anyone can make a smoothbore barrel, but without a rifling twist they will be very inaccurate. This may be fine if you're filling a room with lead with your shop-made Sten gun, but if you want to hit anything at any sort of range you'll need rifling.

Rifled barrels are difficult to make without specialized equipment. Fortunately if you're in one of the countries of the world with a large number of guns per capita, like the US with 1 gun per person (that's 300 million guns), you'll be able to salvage rifled barrels from any number of otherwise non-functional guns. It's easy to take a rifled barrel from another gun and cut it to the desired length to fit, so long as it's the right caliber.

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  • $\begingroup$ I would argue that assault rifles wouldn't be practical until they have stuff pioneered in the early-20th Century like welding and sheet pressing. History suggests that 19th-Century technology was too heavy on resources and labor to make automatic actions cheap enough to be put into small arms. $\endgroup$ – Geoffrey Carlton Feb 14 '18 at 17:30
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    $\begingroup$ @GeoffreyCarlton The lockwork on a typical 16th-century wheellock pistol is more complex and harder to replicate than the simple operation of a WW2-era straight blowback submachine gun. The limiting factor on automatic arms isn't the action, it's the ammunition- centerfire metallic cartridges loaded with smokeless powder are a necessity. If you have a supply of ammunition, a submachine gun or even assault rifle can be built with extremely crude processes. $\endgroup$ – Catgut Feb 14 '18 at 17:37
  • $\begingroup$ @Catgut You make a some fair points. Manufacturing ammunition will be a bigger problem than manufacturing actions for a straight-blowback SMG, but the reason you saw wheellocks before STENs was because you don't need big machines to make wheellocks. Granted, in this scenario you could salvage big machines for making SMGs. I was just pointing out that you would need the industrial capacity before you can make simple, cost-effective guns. $\endgroup$ – Geoffrey Carlton Feb 14 '18 at 17:46
  • $\begingroup$ @GeoffreyCarlton While you're correct stamping requires some industrial capacity, a stamping press isn't difficult and you can do the fiddly bits by hand, it just takes longer. The guns won't be as cheap and high quality as you can get now, but they can make them. The OP mentions they're making steel which requires great investment. Making gunpowder, especially smokeless powder, requires an established chemical industry. Of all the industrial prerequisites, pressing sheet steel is fairly simple. The real problem is barrels, they can be salvaged for a while. $\endgroup$ – Schwern Feb 14 '18 at 19:16
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    $\begingroup$ @Schwern Hey, a quick question! How do you deal with the primer? As every primer needs a working chemical industry to be made. As you said, making a firearm is not an issue. Bigger problem is making a bullet, and, of all things, basically the primer is the problem. $\endgroup$ – Bora Mar 11 '18 at 23:32

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