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I'm creating a world several hundred years after an apocalypse, but am struggling to get the decay of our current civilization right.

The world in short: Earth was hit by an apocalypse in the 2060 (nothing too fancy, just standard nuclear apocalypse with everybody throwing nukes at each other; plus some nanobots going rogue, based on that question). Several hundred years later, world is quite recovered, crowded with changed animals and demons (mutated humans). Humanity barely survived and is still scarce in the world; there are three to four bigger cities all around the world, several small villages, but apart from that not much.

My heroes are traveling through Vietnam and Siberia at some point of the story (Siberia several months or even a year later than Vietnam). Because they need to defend themselves against animals and demons, I came up with the idea to let them find weapons and ammunition stored away in a cache by the Vietcong and (in Siberia) by the Russian army in an old bunker.

My question is split in two parts:

  1. Can a firearm (preferably a handgun of a type used in the the Vietnam War) and ammunition stored away in a cache in the jungle of Vietnam last until about 2650 and still remain usable or relatively easy repairable? How does such a cache have to be constructed? What about a firearm (handgun and/ or rifle) + ammo stored in a Russian army bunker in Siberia?
  2. Can a person repair such a stored gun to fully functional conditions using only handtools that would be carried by a typical scavenger or found in the environment? This might include something like knives or a prying bar, maybe a wire cutter or an axe/ hammer, and also things found in the environment, such as sand for polishing, acid juice from fruits or animal fat. Power tools or workbenches are not allowed.

To make it clear, the weapons don't have to be in perfect condition, just restorable. Any rotten wood like a handle or stock is okay, since it can be replaced quite easily. Rust outside is also okay. Just the mechanism and the barrel have to be in such a condition they can be restored easily. Ammunition should be usable, too.

The required knowledge for our heroes is not the focus of this question, until it would be necessary to restore nearly any part inside using abilities only a gunsmith has. You can expect them to know how to field strip a gun and solve minor technical problems, since they have seen and used guns before. When they came to Siberia, their knowledge might be grown to a level necessary to understand the inner working and mechanics of an assault rifle like the AK.

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    $\begingroup$ According to this answer and a few others to similar questions, ammunition won't survive anything on the scale of centuries without losing its explosive...ness, and it's doubtful that any other components will be intact either. $\endgroup$
    – Cadence
    May 18 '19 at 21:17
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    $\begingroup$ "I'm creating a world several hundred years after an apocalypse, but am struggeling to get the decay of our current civilization right." Grab yourself a copy of The World Without Us if you haven't already. $\endgroup$
    – user
    May 18 '19 at 21:30
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    $\begingroup$ Humanity barely survived and is still scarse in the world; there are three to four bigger cities all around the world Cities are never self supporting and require a large external support network to supply basic foods and even water. If humanity barely survives and is still scarce then the existence of functioning cities (especially in a hostile world) is dubious. $\endgroup$
    – StephenG
    May 18 '19 at 21:51
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    $\begingroup$ they need to defend themselves against animals and demons Their society might naturally develop a considerable proficiency in using more "primitive" weapons. A knife, sword, spear or some kind of bow and arrow are very effective weapons. A sling is another deadly weapon that was used in warfare for centuries. The trope of "leftover" firearms in post apocalyptic scenarios is not the only way to go. $\endgroup$
    – StephenG
    May 18 '19 at 22:07
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    $\begingroup$ The weapons themselves may survive; after all, in real history the Turks fired (for real, in combat) in the 19th century a cannon built in the 15th century. The problem is the ammunition. Ammunition contains compounds which are in a meta-stable state, because the entire purpose is to go boom with little stimulation; having primers and propellants still usable after seven centuries is quite a stretch. $\endgroup$
    – AlexP
    May 19 '19 at 17:40

11 Answers 11

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So many negative thoughts!

Let's put our creative hats on.

  1. Immersed in oil. O2 excluded. What holds the oil? Glazed pottery urns sealed with wax. The oil could be mineral, olive or rice bran. Yes the volatiles may have evaporated and the whole lot set into a nasty waxy mass but I still argue for minimal corrosion.
  2. Stored in an inert atmosphere (nitrogen / argon). Containment will be more of an issue but, say an airtight concrete bunker filled with an inert gas.
  3. For extra insurance say a combination of 1&2.

Of course with option 2 at least one of your party members are going to die when they enter the chamber.

The key factors are going to be:

  • Excluding oxygen

  • Keeping moisture out

  • Keeping it cool

  • Keeping the temp stable

I would also note that modern smokeless powders don't degrade the way black powder does.

700 years is a big ask though.

If I were to create a scenario I'd go for Siberia. Imagine a bunch of pessimistic Russians (who knew?).

  1. They build a bunker in the side of a mountain below the permafrost line.
  2. They line it with concrete so it's airtight.
  3. They fill it with as many AK47's as they can lay their hands on + tools and spares to service. All packed in ph neutral preservative in sealed containers.
  4. They include enough ammo to win a small war (remember standard Russian military doctrine relies on massed fire) similarly packed and sealed.
  5. They pump in Argon until O2 levels are minimal. (Also plays to Russian sense of humour - 'Anyone opening this door is going to get a big surprise, nyet')
  6. They seal the doors and just for laughs bury the whole lot under a few meters of ice and snow.

If steaks good enough to eat can be cut off a mammoth that's emerged from the ice I feel there's at least an even chance some of these munitions will be useable.

Have 'at er dudes

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    $\begingroup$ I'd have more problems believing on someone burying a cache of weapons with such an intrincate scheme that I would on simply believing the weapons just survived 700 years old by chance. $\endgroup$
    – Rekesoft
    May 20 '19 at 10:35
  • $\begingroup$ the products of long term hydrocarbon breakdown are acidic, not something you want to immerse iron in. an open container will allow that to escape but will also allow the material to evaporate and pick up water. Oil and wax are just bad ideas. $\endgroup$
    – John
    May 20 '19 at 13:11
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    $\begingroup$ Hey guys. No argument on the intricacy of the scheme. Just spit-balling some ideas to kick off discussion. Re John's specific comments. Open containers? I specified that the containers be not only inerted but also sealed. I agree breakdown products are a problem. This is one of the reasons the scheme is intricate. By excluding oxygen it was my intention to limit oxidation. Noting also that in sealed containers breakdown products will reach equilibrium levels & so limit further breakdown. Let's not just rain on this parade but think about how we can help the OP make it work. $\endgroup$
    – pHred
    May 21 '19 at 3:09
  • $\begingroup$ Governments and private militia probably do cache weapons underground sometimes, in case an enemy might overrun their position or they might need to fight a guerrilla war. I could see the notoriously paranoid Soviet Union doing so. The Viet Cong of course were overrun and fought us out of tunnels. It is entirely reasonable to believe that there are some 1970s weapons still sitting in a forgotten cavern somewhere down there, although I doubt the containment would be as sophisticated as this answer. $\endgroup$
    – workerjoe
    May 21 '19 at 17:43
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    $\begingroup$ Modern smokeless powder doesn't last as well as black powder, as long as the latter is kept dry (artillery shells from the American Civil War are still found from time to time with the powder inside dangerously functional; WWI vintage smokeless ammo, fifty years or so newer, is virtually always inert due to a combination of powder deterioration and primer compound breakdown). I'd be more confident of powder stored with a flintlock going off than I would of powder (and primers!) in modern ammunition, even in oxygen-free storage. $\endgroup$
    – Zeiss Ikon
    Sep 27 at 18:44
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Not unreasonable:

https://en.wikipedia.org/wiki/Cosmoline

Cosmolene is a mix of waxes and oils. Fresh, it's about the consistency of vaseline or peanut butter. Exposed to air, it hardens into candle wax.

If you can contain it, vaseline can be used. It doesn't turn into gummy crud exposed to air, but even modest temperatures result in it liquefying and running off.

So...

applying this principle:

Take 45 gallon removable head plastic barrels. Pack with weapons. Fill barrel with cosmoline, vaseline or any low temperature melting point wax. Fasten the lid. Plastic (Polyethylene) doesn't rust. I don't think it is subject to creep. It will degrade from exposure to UV light. A barrel full of guns and wax stored in a cave should be good for centuries.

Ammunition. Other sources have mentioned that it would not be good after hundreds of years. Not sure why it would degrade if kept from air. (My suspicion is that the metal crimp at the bullet is not fully air tight, and so air and water vapour very slowly degrade the powder or primer.) If, in addition, you keep it cold, 700 years doesn't seem unreasonable. In general organic chemical reactions have a strong temperature co-efficient, dropping by a large factor with cooler temps. (I recall a vague generalization of a factor of 10 for each 10C change)

Surfing some firearms sites the big problems are indeed oxygen and water. A cool dry environment is best. Oxygen eventually destroys the primers. Eventually water and air and trace amounts of NOx in the air causes the brass to corrode.

Ammunition stored in Pelican cases with a new greased o-ring gasket, with a packet of oxygen absorber, and a desicant packet then closed it with a lump of dry ice in it, vent open, and up. The CO2 sublimes, fills the case with dry CO2, over flows through the vent. Then close the vent. My experience with the pelican cases is that they are airtight. I have had days when without opening the vent, I cannot open the case. I had closed it on a low pressure day. (The cases are good to 30 feet water, and are warranted against everything but sharks and small children.)

More cheaply: The standard military canisters were designed for decades storage, and ones that havent been opened and shut much have very tight gaskets. Just adding a desiccant and O2 absorber to one of these may be sufficient, especially if stored in a constant temperature environment.

The largest degradation in this case would be the barometric pressure changes causing the ammo boxes to 'breathe' each inhale bring a bit of oxygen and water vapour in. a container that could deform with pressure changes might be more effective. Say a plastic gas gerry with caps put on with silicone seal.

Gaskets eventually dry out, lose their plasticizers, and crumble. Again oxygen is the culprit. A film of grease may add decades to their life.

Addition: Zeiss Ikon comments that the primers degrade. And even a small percentage of non-fires will make an awkward pause in combat. Your options:

  • Special run of ammunition that was designed for storage. It occurs to me that you could make a piezoelectric primer that had enough of a recess that dropping a round wouldn't set it off. On strike, it generates an electric spark. Electronic setups have been tried over the years, but are expensive. An ideal system would have the spark generator as part of the firearm,not part of the round. Alternately you could set it off with a dry cell (easy to make) and a capacitor.

  • The weapons stored are modern flintlocks designed to use smokeless powder and minie balls. This would play hell with your rate of fire, but if you have guns and your opponent has rocks or arrows the odds are in your favour.

  • Instead of ammunition, you have an entire production facility mothballed. And while I doubt the ability to keep everything at liquid nitrogen temperatures, I don't think impossible to keep something in a dry inert atmosphere. Aircraft are mothballed in deserts. I don't think the plastic on the wiring would last a long time, but at least there is little corrosion. Mind you, aircraft are mostly aluminum, not steel.

  • Retarded time field. For the ammo it hasn't been 700 years. Remember all the Faerie legends where someone danced the night away in Faerie, and came home to a hundred years having passed? Only the other way. See Niven's Slaver stasis fields.

  • You don't explain it. Your protagonists don't know why it still works.

Edit addressing some comments:

Oils and waxes that are single chain do not degrade very fast. Oxidation on hydrocarbons occurs chiefly at the site of double bonds.

The addition of fillers, such as powdered graphite plates can make the effective distance between the surface of the wax and the surface of the metal MANY times longer. This vastly increases the time it takes for volatiles to migrate out of the mass.

The mention of polyethylene barrels above was deliberate. PE unlike PVC, has as far as I know, no volatiles. In constant temperature with no UV light, I don't see why it wouldn't last forever. As a checkmark, I have 2.7 mil (.0027 inch) black poly tarp that I put in place on a shelterbelt for moisture control in 2005. It's still intact despite 16 years of weather and sunlight. The average wall thickness of the PE barrels I get is about 3/16" or 167 mills. I would be very surprised if it degraded much in constant temperature darkness.

  • A lot of material that was recovered from the Scott attempt on the South Pole decades later was still functional. I don't remember if firearms were part of that, but exposed film was, and it developed normally. Cold preserves.

  • Lot of organic reactions have a doubling in speed for every 10 C (rough and ready rule of thumb) So dropping temperature by 100 degrees would slow degradation down by a factor of 1000.

  • Consider a heat pipe: Take a chunk of drill stem (3/4" steel walls) 100 feet long and cap both ends. Have a single small diameter port. Run into the ground so that only the top 20 feet are exposed. Partially fill with liquid propane. The propane falls to the bottom boiling. (Could use liquid CO2 also) After enough gas has blown off to be sure that what's left is 99.9% propane or CO2, seal the entry port in a way good for a thousand years.

At this point you have a heat pipe that is one way. Whenever the bottom of the pipe is warmer than the top, vapour condenses in the upper part, falls to the bottom, and boils there. Put a ring of these 2 feet apart, around a chamber. Insulate around the outside of the circle of heatpipes. Done properly this chamber will average the 5 year minimum temperature of the location it's in. Given that Siberia has known very cold temps, you have significantly extended the keeping time of your vault.

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    $\begingroup$ Primers degrade -- old "corrosive" military primers are good for forty years or so and stay reliable, up to seventy with "some of these will fire." Modern styphnate are good for, at most, about twenty. 19th century mercurics about the same as styphnate. Nitrate powders similarly, especially if produced under wartime "rush production" conditions. All of these might be slowed by storage at liquid nitrogen temps -- but that isn't going to last centuries in and of itself. $\endgroup$
    – Zeiss Ikon
    May 20 '19 at 13:35
  • $\begingroup$ +1 for cosmoline. I have seen M1 Garands dipped in cosmoline that spent 70 years in the Philippines that looked like they just came off the line. (I have also seen ones that were stored "dry" that were unsalvageable.) Going from perfect after 70 years to usable after 700 is not crazy. Removal does not have to be difficult. One person I know got it off by hanging the gun nose down in his attic all summer. Known-bad primers could easily be replaced by using a drill (it better be bad though). A medieval chemist could probably have made lead-azide if they knew to try. $\endgroup$
    – UrQuan3
    May 22 '19 at 19:52
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    $\begingroup$ Guns, yes, ammunition, no. $\endgroup$ Sep 27 at 0:03
  • $\begingroup$ @UrQuan3 70 years is not 700 years, oils and waxes degrade into acids in that time frame now you have metal stored in wet acid. cases, seals, rubber, and desiccants won't last 700 years, $\endgroup$
    – John
    Sep 27 at 19:05
  • $\begingroup$ A lot of these preparations do seem like the original people storing the weapons are specifically preparing for this story. Also, not sure about the CO2 part. If there was any moister at all in the case upon sealing. the CO2 and moister would create carbolic acid. Cant imagine that would be a good thing after 700 years. $\endgroup$
    – Sonvar
    Sep 27 at 20:52
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If you are at all willing to shorten the timeline of your story, you might be interested to study the history of the Gahendra rifles. These were made in Nepal in the 1880s and stored in the royal armouries. Fast forward to the early 2000s or so and, post-coup, loads of these old guns came on to the market, relatively cheap. Not a bad buy for an untouched century old firearm of somewhat dubious quality.

They clean up pretty well and some people do in fact in shoot them. Without simultaneously blowing their hands off. It can get warm and rainy in the summer, cold and snowy in the winter. But the weapons survived pretty well.

I concur that anything stored in Vietnam will be a heap of rust after seven centuries; and probably even after one century!

But a much better equipped, better constructed Russian facility perhaps with better conditions and higher quality weapons & methods in general might allow for caches of weapons to survive relatively unscathed for a century or two.

Ammunition may not last for 700 years, but it could easily last one to two centuries. Anecdotally, I've read a number of accounts of folks happily shooting off ammo of WWII and WWI vintage.

The key is how well the guns and ammo are stored, and thus what condition the bunker was left in when originally abandoned. If it was carefully evacuated, left intact and locked up and then forgotten about, your characters might just be in luck!

On the other hand, chances are better it will be hastily abandoned, left disheveled and unsecured during the Pockyclypse and will thus be subject to scavengers.

I'd just hate to have to wander all up to Siberia just to find a gun of dubious utility!

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The stuff in Vietnam is toast. Pervasive humidity, warm climates, and storing metals do not mix.

The stuff in Siberia might, might survive, provided they put it someplace that froze over and they used archival grade materials.

Plastics, oil, and wood have volatiles that will outgas, and will produce some reactive elements that will destroy the rest of the gun. The metals in firearms are corrosion resistant but nothing made of iron is corrosion proof. Springs in particular will be destroyed quickly as they can't be made as corrosion resistant and still preserve their qualities.

Guns often constrain multiple different metals which can cause galvanic corrosion, because of this don't expect anything that has been plated or contains more than one metal to survive, this even included stainless steel with carbon steel springs so disassembly is advantageous.

Extremely low temperatures can slow all these reactions to the point properly stored firearms might might be usable with a little work if they were disassembled and stayed cold enough the entire time. Wood parts however will be powder due to the dehydrating effects of cold. plastic will likewise decay in the cold as it crystalizes. Note you still want the parts in sealed containers ice is nearly as bad as water for corrosion.

Remember the firearms were made by the lowest bidder, they were never designed for centuries of storage.

The ammunition is garbage no matter what. Ammunition has a shelf life, reactive chemical in general do not store for centuries. In addition the various metals can actually react with each other exacerbating the process, picture old batteries.

Siberia has its own special issues as permafrost is not static it moves, and will destroy any structure built on it and pulverize anything inside it. there is a reason the seed vault is built in sold rock not ice.

If they were actively maintained over the years instead of stored they may very well be usable as is, but even the best passive storage makes for very poor conditions.

ideal storage for metals (the wood or plastic parts can be replaced) is low temperature, low humidity, no oxygen, no salts, no dust, and surprisingly no oil (oil releases volatiles over long term storage). Ideally any wood or plastic parts will be stored separately otherwise volatile coming off them will corrode the metals. They should be stored in thick sealed inert metal (gold) or glass containers filled with inert gas and even then your chances are extremely low. And you run into the issue that such storage is less believable than miraculous survival in poor conditions.

Sources

Archival storage of metals

Plastic and rubber preservation

Plastic selection

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  • $\begingroup$ A frozen environment that varies in temperature even if its always below zero will experience sublimation which enable corrosion of metals. constant temperature and no air exchange constrains the volatility of plastics since its stops once the partial pressure of the low vapor pressure volatiles equilibrates with the total atmospheric composition $\endgroup$
    – EDL
    May 19 '19 at 7:02
  • $\begingroup$ that is asuming there is water present inside whatever container the gun is in, one of the advantages of low temperatures is the air contains very little water to begin with. the equilibrium point of most of the volatiles are close to the volatiles all being gasses. $\endgroup$
    – John
    May 19 '19 at 12:32
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I also doubt modern weapons abandoned in a cache would still be usable in 500 years. But I used to work with a gentleman who made reproduction 18th century duelling pistols for fun - starting with a block of wood and 3 blocks of metal and only using handtools and techniques from that era.

Maybe instead of a military bunker your heros could discover a museum with similar reproduction pieces? Modern steels might well last and be useable if replacement woodwork can be made. Gunpowder would be sufficient and is relatively low tech so possible they could either have some already or also rediscover the recipe.

[Officially the guns he made were inactive. Unofficially they were authentically accurate, although it turned out that powder from shotgun cartridges was a bit too powerful.]

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  • $\begingroup$ I agree with Zeiss Ikon that chemically the propellants from current firearms are too chemically unstable and will spontaneously decompose (O2 or not) in 700 years. A museum filled with antique black-powder rifles sealed in a preservation facility and even the black powder itself would surprisingly be a good choice for your survivalists, since black powder really is pretty inert stuff. So a sealed room underground flooded with argon - and probably steel swords, weapons to boot - possibly armor as well. $\endgroup$
    – DWKraus
    Sep 30 at 1:22
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I want to address the second part of your question:

Can a person repair such a stored gun to fully functional conditions using only hand-tools that would be carried by a typical scavenger or found in the environment... Power tools or workbenches are not allowed

While it may not work as well (and probably missing some major features), I am confident in saying this is 100% possible. Improvised fire arms have been made from almost literally everything made of metal.

Basic examples:

This is a Brazilian improvised firearm made from a paintball marker (there is even an office chair tilt knob for cocking handle).

Here is a gun made from a metal table leg.

These Swedish guns were made from boat components and a pipe.

This trash bag full of handmade zipguns was turned over to Mexican officials in exchange for cash and amnesty.

This beautifully hand-built gun was turned over in the same buyback program.

Here are some guns found when a Japanese was arrested after producing improvised guns for over 40 years. (full article with more pictures)

These were used in an assassination attempt on a South Korean official, they are almost literally just pipes taped to wood.

Converting old flare-guns into pistols seems to be a favorite of criminals in India.

This gun was made to emulate the famous AKM despite only being bolt action.

Semi ironically these eoka type pistols were made by African colonies from the expended 20mm cartridges of their oppressors.

More complex examples:

Groups in The West Bank have been covertly producing The "Carlo SMG" which has been used in many terrorist attacks.

Improvised Sten Guns have been made across the world from the IRA to Yugoslavia to Guatemala. (The one pictured was made from just an angle grinder)

Similarly The "Błyskawica", based off the Sten was widely used by the Polish resistance during ww2. (Top is Błyskawica, bottom is Sten)

The "Borz SMG" was widely used by Chechen Separatists as a crude semi-disposable weapon to ambush police and military forces, after which they picked up whatever guns they could find.

P.A Luty famously/infamously wrote a book claiming it was impossible to ban guns because people would just make their own, then explained how he made this gun from scrap metal and hand tools (Image is of a modern copy made from his book).

Summary: This is all to say without a machine shop, a gun can be easily made. Anything that could be salvaged that resembles a gun would make for an even more effective improvised weapon


Bonus:

Nerf gun conversions from South Africa

Homemade AK like smgs from Bangladesh

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  • $\begingroup$ I would contend, after 700 years with no large scale manufacturing and spreading of knowledge, it would be difficult for a person to understand how to repair a 700 year, highly complex tool with crude tools. $\endgroup$
    – Sonvar
    Sep 27 at 21:00
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They Would Require a Modern Machine Shop to Restore

20th century firearms were machined to very tight tolerances (typically 1-3 1000ths of an inch). This means that all the moving parts are always in a state of being pressed together. Even if you stored these guns in a perfectly inert environment, within the first few decades of not moving the metal parts of the guns will begin to cold weld together such that after 700 years all the metal parts will become one contiguous block of metal.

This means that at the very least, you would need to drill all the screws out, drill out the firing pin, and cut through fussed seams, just to open it up. Then you would have to meticulously clean it, probably re-bore the barrel, and mill new screws, springs, and firing pin. You'd also need to tap and die new threading to screw things back together.

This could all be done with the tools a sedentary scavenger might keep in a small workshop somewhere if he could figure out how to get a working metal lathe, but not with stuff you could just carry around on your person. If you tried to do this with hand tools, your tolerances would be too large and you'd ruin the firearm.

More Reasonable Scenarios

The weapon cache may be much less than 700 years old even though the weapon designs are older. I know a few people who still own and fire 175-200 year old fire arms. The trick is that these guns never stopped being taken care of. They have been routinely cleaned and repaired since they were manufactured so they've never had the opportunity to cold weld into a solid block. If these weapons had been maintained by hand tools for the past 700 years, they may still be in working order.

I also know people who fire recreations of 300 year old firearms. The other thing to consider here is that there are simply too many people in this world who understand machining and firearms to think that a nuclear war would completely destroy the firearms industry... but it could make them a lot more rare. Firearms would become a cottage industry like they were before the 1800s. So, you may have professionals with tools for making and maintaining fire arms who could have continued manufacturing firearms in a similar fashion to 20th century weapons. In this case, the weapons may be modeled after an AK-47 or what not, but actually be much newer than that.

The other solution would be to find a 700 year old workshop along with the bunker. As I suggested before, the tools needed to maintain, or even make a firearm are not all that complicated. Unlike a gun, the components in the tools you will need like a metal lathe or a press are mostly going to be either non-touching, or in configurations that make them fairly easy to torsion free if they do become slightly fussed. The hard part here will again be the lathe. It needs a working motor; so, your protagonist will probably need to improvise something to make it turn. Once he has restored the workshop, he could also restore the firearms.

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I have no problem with the guns being functional if they were packed with long term storage in mind. As for why--some governmental organization hid them there as supplies for special forces units to operate while out of touch. Such weapons would be packed to last and well concealed--they were found because ground movement exposed the cache.

Unfortunately, chemical ammunition inherently contains highly reactive chemicals. Highly reactive chemicals will degrade over time no matter how tightly you seal them up. (As will the power sources of any guns that work with inert ammunition.) The only way you can slow this process is with cold--and nowhere on Earth do you have enough natural cold for what you're trying to do.

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Not impossible.

Prepare several large fish tanks in a bunker in Siberia. Cold, but not extreme cold. The bunker is suitably armored.

Make the fish tanks airtight using silicone. You have now containers made of glass and silicone, both very, very long-lived.

Place the weapons in the tanks, disassembled and cleaned for safety, then flood the tanks with nitrogen gas. The silicone seal ought to be amply sufficient to keep the gas inside. Do not forget to put manuals inside, with lots of easily understood pictures.

After the tanks are safely flooded and sealed, a simple clockwork mechanism will open an asbestos-lined copper heat exchanger filled with sodium (also in nitrogen atmosphere) to the internal atmosphere of the fish tank.

Now, not only will the fish tank stay oxygen and water vapour free, but any stray molecules that might come inside will be quickly absorbed by the sodium. Like silica gel, but more evil.

When someone opens the tank, the exchanger will erupt in sudden but short-lived flame, but that might add to the spectacularity of the discovery.

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  • $\begingroup$ sodium is going to damage the metal, and water that the sodium absorbs will release heavy alkali ions over centuries, and destroy the metal. combined with the copper it will also give the glass a charge which could do strange things to the metal. better to leave it out entirely or use a more stable desiccant like archival desiccated paper or desiccant clays. Also argon is better than nitrogen, nitrogen is still reactive. $\endgroup$
    – John
    Sep 28 at 17:21
  • $\begingroup$ @John I am not suggesting putting the sodium in contact with the metal of the weapons, just in the same atmosphere inside an appropriate crucible. Yes, argon would be better, but N2 is next to inert, easier to obtain, and less likely to outgas through the silicon. $\endgroup$
    – LSerni
    Sep 28 at 17:50
  • $\begingroup$ I am not suggesting it is in contact, just connected to the same atmosphere. which over 700 years is close enough. $\endgroup$
    – John
    Sep 28 at 18:30
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Firearms made early than the 18th century had very poor quality steel and poor methods of preservation for the wooden stocks. They had very short lifetimes, especially on the battlefield when exposed to wind, rain, mud, and blood. But today, people collect weapons that were made in the 18th and 19th century, and they are still functional. That's because people learned to make better steel and learned how to preserve the wood.

Today, we know how to make awesome steel and other alloys with high hardness and corrosion resistance. Under ideal environmental conditions, firearms that were high-quality plastic and metal construction, like an M-16, would be either viable or repairable. The lubricants exposed to air would have broken down, and the slides and receiver might stick, but cleaning and lubricating and working the mechanisms should make them operational. It's possible that springs might weaken, too. But, I would expect a cache would have a small set of tools and replacement parts of wear-prone items.

If the weapons were standard "dirt cheap because they are made of dirt" AK-47 then I would expect that they would be less likely to survive without corrosion and rot making them unusable.

But, assuming ideal conditions, many disfunction weapons might be torn down to make a few functional weapons.

So, an arms cache buried in a hole during the Tet Offensive would not provide ideal conditions. But a command bunker for the government types might. It could conceivably be sealed against humidity and deep underground where the temperature is low and stable.

For Siberia, I would think that Modern Russian caches and depots are as well designed as anyone else's caches and depots, and the weapons would be in good condition.

The ammunition will degrade if the temperature varies and humidity is high. So as long as the packaging is intact and everything was cool and dry, it would last for a very long time. ANd, the muzzle velocity produced by the ammo would be reduced, and some rounds might not provide enough kick to support semi-automatic fire -- they jam instead. But, manually racking a round would still work

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    $\begingroup$ Even high quality steel will rust away to nothing in a humid environment after 700 years. Springs in particular because of the composition are very vulnerable and difficult to replace. wood and plastic have volatiles which will outgas over hundreds of years. $\endgroup$
    – John
    May 19 '19 at 2:46
  • $\begingroup$ rust needs oxygen, and good preservatives are designed to prevent the ingress of that. $\endgroup$
    – bukwyrm
    May 19 '19 at 9:49
  • $\begingroup$ I think you've got the life expectancies of M-16 family and AK-47 family backward. M-16 is a close tolerance design; it'll start to fail just from getting dirty after firing a few magazines (this was worse when they were new because of the propellant used in the ammunition at first). AK-47 are loose tolerance -- less accurate out of the cosmoline, but very tolerant of dirt, mud, snow, corrosions, and failure to clean and lube. $\endgroup$
    – Zeiss Ikon
    Sep 27 at 19:22
  • $\begingroup$ a long time is not 700 years no cartridge is surviving 700 years no matter how you store it, the propellant is reactive and will react in that time frame likely destroying the case in the process but definitely rendering it no firing. lubricant breaks down into acid over this time frame, oiling them is more destructive than not over this time frame. $\endgroup$
    – John
    Sep 28 at 14:26
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I think both regions could use the same scenario to provide what you need.

As others have said, the primary issue is going to be general exposure. Oxygen, moisture, humidity, etc. If any of this is present your scenario becomes far less probable with a 700 year timeframe. So we have to get creative.

Let's shift our thinking a bit and say they don't find guns and ammo. They find something akin to a parts cache where they can assemble guns and ammo.

Many weapons of this era are polymer already, so a wealth of the components for the frames and furniture could conceivably be in tact with little or no damage.

Ammo would be useless, and if it wasn't, you wouldn't trust the fail rate on what you find. Each pull of the trigger would be like pulling the arm on a slot machine. But the components to load ammo could easily exist depending largely on how the propellants were stored, or happened to be preserved.

Suppose you found an old hunter's lodge in the siberian wilderness that happened to fall below the surface during some freak oil supply run accident that manages to submerge the lodge in ruins beneath the ice and snow, in a pool of oil, freakishly covered and pressured with plastics, or whatever. Suppose the siberian hunter was a nut for oxidation or whatever, and kept the rifles broken down, separated, and air sealed. Barrels, springs, schematics and everything. The hunter had a reloading bench with dies for all the weapons in his own cache, so if you find all that, you may also find the cheat sheet all ammo reloaders keep with their bench, though most hand write that data and the legibility and info may not be as useful (which could help your story).

The propellant is a weird one because on the one hand, common gun powder could be made, but your crew would have to know how to do that. And standard loading propellants are almost positively not going to remain effective over this period of time in just about any version of preservation. It has to be dry, cool, and it can't be in a place where expansion is prohibited. Plus, even if you solve the propellant one, you have to consider the primer. So if making bullets is a thing you want your crew to do, you may have to dig in to seeing how one would make a home made primer and home made gunpowder, and see if those resources are reasonably available in your story.

But also consider this. Even now gunpowder is practically ancient. No matter what happened in life, and no matter how few people remain, it might be hard to erase the knowledge of this sort of chemistry. Inventing gunpowder and primers may not even be an issue in your world.

But thinking of how a building collapses, you could have plenty of well preserved things buried in a chamber where the air around is not problematic as the layers it has been covered in may be the preserving agent, and the junk pile beneath is more or less a collapsed hoarder's room. The broken down guns and reloading equipment was always stored responsibly, in cool, dry ways, with silica, oils, and whatever. And now they are covered in more protection. Just now they are well beneath the surface in something of a nasty honey cocoon waiting for your crew to accidentally knock the right boulder loose and cause a chain reaction that uncovers a few nice treasures.

In short, you don't find something that was designed to store weapons. As others have said, if someone knew, it would have been raided or unearthed long ago. Yours might benefit from something closer to an accident that overturned a corrupt officer's personal convoy into a convenient sinkhole in just the right conditions to both preserve the contents of the convoy, bury them, and cause no reason for the people of the time to seek answers and hunt it down. War time tragedies. It happens all the time.

Whatever your scenario, you may also be able to get away with not over explaining the hows and whys. Considering that a gun can be stripped down, and regularly are, then the idea of a combination of surplus, polymer, old timers documenting their recipes and things, and reloading supplies, you could conceivably uncover enough parts and supplies to assemble several functional firearms, or like piecemeal ones that technically function, are probably not as effective as they once were, or operate in single fire mode because of x, y, or z.

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  • $\begingroup$ none of that will survive 700 years, metal and paper will be useless, no cabin will last that long, oil will destroy gun parts over hundreds of years, oil degrades and is actually worse than not having it over that time scale. even plastics will degrade after that long. $\endgroup$
    – John
    Sep 27 at 19:01
  • $\begingroup$ @john - The cabin didn't last that long. What's saturating the debris is what is preserving the contents. Nothing is just exposed. Everything does degrade, but at what rate depends on tons of factors, and the OP's question is not asking for the perfect preservation formula, but whether or not such a thing is conceivable. It is possible. Not probable, and I am not attempting to provide the chemistry or means for preservation, but I will not go so far as to say such a scenario is just outright impossible given we have plenty of impressively preserved archaeology surrounding us today. $\endgroup$
    – Kai Qing
    Sep 27 at 19:18
  • $\begingroup$ impressively preserved means still recognizable not still usable. this is what 700 year old metal looks like in the arctic. westerndigs.org/… $\endgroup$
    – John
    Sep 28 at 0:37
  • $\begingroup$ That's what 700 year old weapons look like in containers and preservation means of those eras. We're talking about modern storage and I am suggesting the OP encounters equipment specifically designed to withstand the elements, stored in ways that may have survived on a doomsday prepper level and happened to be toppled in a way that allows them to be covered in additional protection - akin to the concept of jurassic park. Impossible, or improbable as any of it may be, it would be nice to have counterpoints with actual scientific backing. $\endgroup$
    – Kai Qing
    Sep 28 at 3:44
  • $\begingroup$ It's not like i genuinely believe any gun component would be usable after such time. But that I am not so willing to dismiss that there isn't some strange level of happenstance that could give enough to work with and that it is not in the form of a fully assembled, locked and loaded gun. Enough to be able to fill the gaps like springs and screws, firing pins, and other things that could be fashioned to make more specifically designed components work. Who knows, maybe a warlord hard chromed a 1911 and stored it in pieces vacuum sealed and stuck in some preservation chamber. $\endgroup$
    – Kai Qing
    Sep 28 at 3:50

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