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In Die Hard 2, there is an infamous scene where the protagonist talks about the fictional Glock 7 that was used against him. Apparently, it was a porcelain gun made in Austria Germany that didn't appear on metal detectors or X-rays. It is also very expensive.

To gun nuts, this sounds silly. However it got me thinking, is it actually possible to make a firearm with modern technology that is:

  1. Concealable (it can't be a huge rifle or machine gun, more like a handgun).
  2. Can't be detected by metal detectors

A non-metallic gun seems like an obvious solution but good luck making a viable firearm that isn't made out of metal. You can also try using non-conducive metals but they also generally make poor choices for firearms. Also remember, not only does the gun have to be immune to detection but the bullets as well; which just compounds the issue.

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    $\begingroup$ When you say "gun", would a single-use firearm work as an answer? Perhaps it might be helpful to define the limits of what you mean by gun so we know what the constraints are. $\endgroup$
    – Escaped dental patient.
    Oct 23, 2022 at 21:44
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    $\begingroup$ I know it was in the dark recesses of ancient history, but wasn't there a rather touching media emotion in 2018 or thereabouts about an American gentleman who attempted to share freely on the internet the description files which would enable anybody with a good 3-D printer to print their own undetectable handgun? For more details see Defense Distributed on Wikipedia and elsewhere. You are asking a question about something which has already happened. $\endgroup$
    – AlexP
    Oct 23, 2022 at 21:59
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    $\begingroup$ In the line of Fire features John Malkovich, a villain bent on assassinating the President of the US, who creates a pistol from epoxy or resin. There's quite a bit of scene depicting him make, use, and conceal the firearm. $\endgroup$
    – user458
    Oct 23, 2022 at 22:01
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    $\begingroup$ @fredsbend Well, when you say hard you mean abrasion resistant which is not what you need. You need something that won't break or shatter, so strong or tough. Your link says as much. If you need it to work once getting worn won't matter, but not blowing up in your face certainly does. $\endgroup$
    – DKNguyen
    Oct 24, 2022 at 2:49
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    $\begingroup$ Are you asking us to help you break the law? In the real world, I mean? I hope not. $\endgroup$
    – RedSonja
    Oct 24, 2022 at 12:36

15 Answers 15

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It comes down to what counts as "detectable".

We already have 3D printed guns, but you need a few metal parts: The bullet, the cartridge, the primer and what hits the primer. Let's see what we can do with these:

  1. Bullet. There's not really anything we can do here, anything that will be an effective bullet will be dense metal. However, note that it's non-ferrous metal, a bullet itself isn't going to set off a typical security metal detector.

  2. Cartridge. Guns existed before cartridges existed, we don't need them. When you're printing your gun you block the barrel with a very thin layer across the barrel. 3D printed guns are basically single-shot anyway, this isn't a big problem.

  3. Primer. We will have to sacrifice a bit of safety here. Without protecting the primer it will be easier to fire it by accident.

  4. Striker. Let's carry this very openly--print your gun to use a key as it's striker. Put the key on your keyring. Security will see it but not recognize it.

Note that while this will get past typical metal detectors this will not get past modern x-ray. It will show as a large mass of organic material and that will be checked to ensure it's not explosives. A 3D printed gun is big enough that you will normally have to send it through the x-ray rather than carry it through the metal detector.

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    $\begingroup$ 2 and 3 can be easily made out of plastic as well. They're just out of metal because that's the most cost effective material. No need to get rid of cartridges or safe primers, they just cost 10 times that because you need expensive plastics $\endgroup$
    – Hobbamok
    Oct 24, 2022 at 9:02
  • $\begingroup$ @Hobbamok I was picturing not having a cartridge at all, the gun simply contains a space with the gunpowder. $\endgroup$
    – Loren Pechtel
    Oct 24, 2022 at 22:33
  • $\begingroup$ @Hobbamok, 3d-printed gun barrels don't last more than a few shots, so you might as well make the gun barrel act as the cartridge and replace it after each shot. $\endgroup$
    – Mark
    Oct 25, 2022 at 0:30
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    $\begingroup$ Where did you come to conclusion that non ferrous metals do not trigger metal detectors? One of the most triggering things are aluminum sheets... $\endgroup$
    – Tomáš Zato
    Oct 25, 2022 at 11:31
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    $\begingroup$ @TomášZato Non-ferrous metals do not trigger them as much, the quantity of metal in a bullet isn't going to set them off. Even a wand at close range doesn't react to my wedding ring. $\endgroup$
    – Loren Pechtel
    Oct 25, 2022 at 22:31
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You can 3-D print guns

We use metal for a reason, plastic can't handle gunfire very well, but you can 3-D print a plastic gun. It'll probably if you're lucky handle a few shots before breaking.

You'll need to conceal the plastic in other plastic

Consider inserting it into the wall of a suitcase. X-Rays can detect density, and can detect guns. You want it to not look too gun like.

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    $\begingroup$ You would have to bring non-metal bullets though (if the OP wants to) $\endgroup$
    – DialFrost
    Oct 24, 2022 at 0:03
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    $\begingroup$ Concealing a bullet or two on some other metal object like keys is a lot easier than concealing a gun. You can only fire one or two bullets so that's fine. $\endgroup$
    – Nepene Nep
    Oct 24, 2022 at 0:07
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    $\begingroup$ Why use a plastic gun when a wooden gun is much more useful. $\endgroup$
    – Daron
    Oct 24, 2022 at 0:12
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    $\begingroup$ Worth adding that while a plastic gun will get past metal detectors, X-rays still have the potential to pick it up. The biggest variable in X-ray scanning detection is the alertness of the operators - in a tiger test some years ago an airport security officer who had been on duty for hours failed to notice a disassembled handgun passing through in a bag, then failed to notice the assembled handgun in a bag, finally failed to notice the handgun simply going through on its own sitting on the conveyor belt! $\endgroup$
    – KerrAvon2055
    Oct 24, 2022 at 1:06
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    $\begingroup$ Using a paper cartridge (as popularized in the 17th century) with non-metal shot instead of a standard bullet would eliminate another detectable source of metal, as would using something like a matchlock firing mechanism. Old black power rifles - while still lethal - have lower muzzle velocities and lower internal pressures, which would help your plastic parts survive longer. $\endgroup$
    – bta
    Oct 25, 2022 at 18:12
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Don't hide it; disguise it. Instead of having a gun that doesn't ping a metal detector or show up on an X-ray, have a gun that doesn't attract any suspicion despite being seen and known to have metal parts. Your gun (or the metal parts of it, if you can assemble the gun after the security checkpoint) could be made to look like a walking cane or crutches, a musical instrument, sports equipment, or a workman's tools. The bullets could be made to look like jewellery, electronic components, or machine parts.

This won't work if you need these guns to be common in your world, because security staff will know about it and learn to be suspicious of things which guns are commonly disguised as. But if your story only needs one or a small group of clever characters to get their guns past security, then it's more plausible.

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    $\begingroup$ As in 007's The man with the golden gun, where Scaramanga assembles a gun with what looks like a cigarette lighter, a fountain pen, a cigarette case,a cufflink and a bullet - see thefirearmblog.com/blog/2019/09/13/007-golden-gun $\endgroup$
    – 今夜九
    Oct 24, 2022 at 19:37
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    $\begingroup$ In the novel The Day of the Jackal, the assasin used a rifle disguised as an aluminum crutch. Single shot reloadable. Not sure how the movie treated this. Book went into some detail about the gun. en.wikipedia.org/wiki/The_Day_of_the_Jackal $\endgroup$
    – FlaStorm32
    Oct 25, 2022 at 0:38
  • $\begingroup$ "workman's tools" are actually on a list of prohibited items when flying (at least in EU, IIRC) and may be stopped by security. $\endgroup$
    – Frax
    Oct 25, 2022 at 23:10
  • $\begingroup$ @Frax: That might have some overlap with knife laws, where it's not uncommon for laws to state an exception to laws against knives if they are tools for your profession, presumably to prevent brick-layers from getting hassled for sharp trowels. $\endgroup$
    – Sean Duggan
    Oct 26, 2022 at 14:21
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    $\begingroup$ @Frax That's a reasonable point if the gun has to get past security at an airport, but the question doesn't specify an airport; security checkpoints exist in other places (e.g. I once had to have my backpack X-rayed when using the subway in Beijing). Additionally, airport security might need to allow contractors to bring their tools past security if they are there to work at the airport, rather than to board a plane. $\endgroup$
    – kaya3
    Oct 26, 2022 at 14:51
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If it can be a small caliber, single-shot pistol, and the scenario is that such guns are rare (i.e. cops aren't on the lookout for them), then the guns could be custom-made... in steel or whatever is the standard metal for firearms.

Yep, super obvious and it's going to trigger all metal detectors and x-rays.

However, the gun comes encased in a precision-cut slab of the exactly same metal. The slab matches the gun's profile perfectly, leaving no voids when the gun is inside. So, from the outside, the slab is just... a small iron slab.

The slab is, however, designed with intricate carvings and since the gun hidden inside is so small, you can tell the TSA it's a paper weight or a family heirloom or something. The carvings however also serve to distract from the ever-so-slight seams. Once you're past security, a complex series of pushing, pulling and twisting causes the slab to come cleanly undone, granting access to the weapon within.

Now, might the TSA wonder why you're carrying a pretty steel slab around with you? Sure, they might. But then again, they're the TSA. They're used to dealing with the weirdest of the weird, some wacko carrying a small hunk of steel around will be the most normal thing they've seen all day.

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  • $\begingroup$ Well, I had to travel several times with some big lumps of metal in my carry on, nothing gun related (it was just casing for electronics). I got inspected in detail every time. Once, one of the officer explained to me: "when we see a big lump of dense metal... we check." They are used to deal with weird, but they get extremely curious to weird they haven't come accross before. And it will take long explainations to get the weirdness out of the way. If your slab is a concealed weapon, you'd better make sure you can also demonstrate it to be something else (decoy) otherwise they will find out. $\endgroup$
    – Hoki
    Oct 26, 2022 at 9:56
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Stainless Steel guns

Unfortunately this can be detected by metal detectors but sometimes it won't, so it might be a viable choice. Stainless steel has very low electrical conductivity and low magnetic properties.

However if the metal detector is not configured correctly it usually can't detect this.

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    $\begingroup$ you can also combine this with the 3-D printed plastic gun answer: a couple of the critical parts are indeed made of this steel, but 99% of the gun isn't, giving you the best of both worlds $\endgroup$
    – Hobbamok
    Oct 24, 2022 at 9:00
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  • Metal Detectors or X-Rays?
    It is hard to imagine something like a firearm that does not show up on x-ray. The barrel and the bullet need some reasonable density, and that will show up.
  • How many shots, how reliably?
    A decade ago ago, a German IT magazine teamed up with a gunsmith to test 3D-printed guns. Back then, their conclusion was "impractical." First it did jam, then some adjustments, jammed again, more adjustments, finally it fired, then it was worn out. Since then, printers have become better.
  • How much custom gunsmithing?
    A ceramic (or dense plastic) bullet, in a plastic cartridge, with a ceramic firing pin hit by a plastic hammer. Possibly a derringer-like construction with one shot per barrel.
  • How little metal can be detected?
    If some wires and batteries are in the cards, electronically fired superposed loads might be an option.

The first bullet point will be decisive, unless the character knows that only metal detectors are used.

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  • $\begingroup$ Cartridges among a set of full-graphite pens (all styled to look the same) in a lead-clad pencilcase, 95% chance of getting through $\endgroup$
    – Hobbamok
    Oct 24, 2022 at 9:04
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A perfectly concealed weapon would be a non-metallic, roughly dildo-sized gun inserted in your anus. It is undetectable by any means short of a cavity search.

It would be triggered by tightening the sphincter muscle around a contact when bent over, after squeezing it out a bit, like a turd (it will cause a desire to defecate anyway).

The recoil is limited so that it does not rupture your lower intestine when shot. The device can have some mass, limiting its recoil, so the projectile should have enough energy to kill someone.

After firing the gun you'll run around with an embarrassing hole in your pants and underpants but that will likely be the least of your problems.

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    $\begingroup$ And how would you go about aiming that? Anything further than point-blank range and your chances of hitting your target with a bullet out the backside are slim-to-none... $\endgroup$
    – Darrel Hoffman
    Oct 24, 2022 at 15:20
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    $\begingroup$ @DarrelHoffman True! Judging by the condition of some public toilets aiming is really hard! $\endgroup$
    – Peter - Reinstate Monica
    Oct 24, 2022 at 15:39
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    $\begingroup$ Given the amount of methane present in such an environment, this design has some interesting ways to backfire. $\endgroup$
    – bta
    Oct 25, 2022 at 18:15
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What about a toy gun? There are very realistic toys on sale. It should be custom made and it should be able to fire like a standard nerf gun. But, at the same time, it could be made to fire a small caliber bullet through a second small muzzle which is an ornament for the main one. Someone brings that gun and someone else on the plane brings two or three bullets. To disguise it better, they should package it as a gift for a kid whose picture is supposed to be in the wallet of the gunman.

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    $\begingroup$ And because there are very realistic toys on sale, security will never allow them on aircraft, just as they don't allow realistic-looking plastic knives or pens made from cartridge cases or anything that would facilitate this kind of deception. This was true even before 9/11, you're just asking for trouble trying to carry that kind of thing today. $\endgroup$
    – KerrAvon2055
    Oct 24, 2022 at 14:05
  • $\begingroup$ @KerrAvon2055 That is a good point. I better study more the ways to deceive the TSA. like disguising everything as a baby formula bottle. $\endgroup$
    – user3653831
    Oct 24, 2022 at 16:05
  • $\begingroup$ @KerrAvon2055 That's why you use one of those laser light gun toys that used to be so popular but you can't find anymore. What ever happened to hose? They lit up and blinked and made sounds and stuff. As I recall, they were all unusually heavily built as well. $\endgroup$
    – DKNguyen
    Oct 25, 2022 at 0:26
  • $\begingroup$ If this plan requires you to take out and show a photo of a child from your wallet, then you know you're not going to survive this movie. So this is only available to people willing to die for their cause. $\endgroup$
    – Ben
    Oct 25, 2022 at 5:27
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In the movie "In the Line of Fire", the assassin had made an undetectable gun (see replica). Basically, used springs from ink pens and plastic for the gun. He hid the two bullets inside a lucky rabbit's foot on his keychain. With modern 3d printing and the innocuous nature of the key chain and pen, it seems like a completely viable way to circumvent metal detectors. The keys don't even go through the metal detector nor the pen(s); no one would likely bat an eye at either item.

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If firing a single bullet is enough, a reasonable gun and bullet can be made out of glass.

A thick enough glass cylinder will withstand the pressure. Glass can be ground to air tight tolerances as is regularly done with laboratory equipment.

A glass bullet will not be as dense as a metal bullet would be, but at close range enough energy can be delivered. When the bullet shatters on impact, the shards will increase damage caused.

If a mixture of flammable gas and oxygen is used instead of gunpowder, the glass container will appear empty. It could be disguised as an extra robust gas syringe or some medical device.

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I would suggest making a plastic pistol that uses elasticity to propel the bullet. The plastic could be used for the stock and other parts of the gun. However, the problem is power. Such a gun wouldn't be able to have a large impetus behind the bullet. However, some elastic materials can have lots of potential energy, which means that it can send a plastic bullet traveling very fast. Make the plastic bullet sharp, and it will pierce flesh. Again, it won't have the power to go through bullet proof vests, but it will work well for assassinations. The plastic should be hard and strong. If your character can make such a gun, then it will be concealable but still somewhat lethal.

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    $\begingroup$ At some point this becomes more of a crossbow $\endgroup$
    – Jiří Baum
    Oct 25, 2022 at 7:07
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    $\begingroup$ @JiříBaum yes i know. But using a traditional gun that is powered by an explosive charge to launch the bullet, without using metal... well, that would likely blow up the gun. Alternatively, one could just use a heavy plastic knife. $\endgroup$
    – user99163
    Oct 25, 2022 at 12:37
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Plastics as strong as steel

Plastics are incredibly versatile. Though they have polymers as a base, it is incredibly diverse. So diverse it is actually a bit weird putting them under a single umbrella. You can have plastic that is great at moving a current surrounded by plastic great at insulating the electric wire.

In that vein you have plastics that are as strong as steel. I do not know of they show up on scanners, but one or two were promising in at least being much lighter than steel. This kind of compound seems difficult to make and mistakes easily lead to weak materials, but technology advances to reduce it to next to zero. And even if these are picked up by scanners we can use different plastics. If those aren't available you can add a replaceable tube that needs to be changed every x shots.

It doesn't seem a stretch to then just make very expensive plastic guns. Having them as plastic already eliminates the scanners, sort of. If you look at scanners you'll notice you can also identify a lot of other stuff that isn't metal. So unless you find a way to keep it on your person it might still be detected. So you need to change the shape to something inauspicious, or have it blocked ny something. Like putting it into a thick laptop where battery and electronics hide the true nature.

Do note that if you keep it on your person they can still check you on items. Many scanners show areas where there is something weird. I've been searched more than once just for having an extra layers of clothing that was positioned strangely. I'm guessing it has to do with tightness of clothing. A gun can stand out.

Simply do not get scanned

Why make a weapon that is undetectable and go through security? You run the risk of being picked out just from your behaviour, random check or sheer bad luck. At the airport I used to work even the employees need to go through a security gate. It is a little more relaxed, but still very thorough. That being said there are ways known not to get scanned and still get behind the gates. If you do it right you can walk into an airfield armed like rambo with rocket launchers, heavy machine guns and grenades without ever seeing a security gate. I'm not saying it is easy, but it is certainly possible.

Make weapons beyond the gate

It is interesting how they prevent weapons from coming through, but you can make weapons from stuff you can buy beyond the gate. They even sell things that unmodified can be used as weapons for stabbing or slashing, not to mention to just club someone. But someone once tried to prove a point you can go beyond this, making a bow and iirc even a crude crossbow from stuff available in the shops.

So if you want to ultimate concealed weapon, have none. You can be nervous, picked out of a line, random security checks and a freak disaster leaves you naked with the contents of your suitcase all over the floor. They won't find anything as you don't have anything. As long as you have your credit card you can build a weapon beyond the gate and do whatever.

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Composites.
Carbon fiber is stronger than steel. If you wrap it around the outside of a plastic "bullet" then you get a plastic object that has a primer in it. The size visual footprint is about half the size of a bb, and any human doesn't have a cognitive hook to catch.

Whiskers are much stronger than bulk materials. Consider titanium or tungsten whiskers in your composite. Perhaps in a cermet.

MetaMaterials/Stealth.
X-rays tend to be harder to steer, but they can be steered. The RF/Microwave wand used for metal detection, is nearly trivial to steer. So you make it not see, not see much, or have it cause the waves to self-interfere.

Comment.
I remember how Speed(1984) predated the prevalent bus-bombings of the second Intifada. While I can think of 20 ways to solve the problem, posting those in a public forum like this is uncomfortable, and ethically problematic.

Don't kill people. Murder is a sin. A man can say it has no consequence, but if you soul knows its wrong, then do not do it even on pain of death; every man who speaks only for himself and wants a religious audience claims (falsely) to speak for God, while only a few speaking actually for the will of God make such a claim. Question those who say it is good. Examine them carefully.

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What else could you conceivably carry that could be detected but not set the TSA into worry mode? Batteries to me seem a good possibility... nice metal case, full of X-ray dense stuff. Customise a radio that uses (for instance) two AA batteries to carry an extra 2 AA batteries that are not part of the original circuitry. Make the caps of the batteries removable such that the two tubes can screw together for a barrel, build the trigger mechanism so it fits on one battery body and ammunition (single shot... maybe two shots) in the other. And once you assemble it you've got a 3V supply as well for electrical firing so the trigger could be as small as a simple push switch. And if you need extra disguise... the two 'real' AA batteries that prove to the TSA it's just a radio... and it turns on... could be heavier gauge shells with AAA cells inside so they look similar to X-ray to the gun parts

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High-tech ceramics?

I don't actually know whether this is feasible. High-tech ceramic materials can be astonishingly tough, but all ceramics do tend to be brittle. However, Piklington glass once made a commercial in which a glass hammer was used to hammer in a nail and them (more remarkably to myself) to claw it out again. And that was just toughened glass, not anything really exotic. Jet turbine blades have been made of ceramics. (Maybe still are, that'll be classified info. What little I know says metal "superalloys" now rule that roost).

Intrinsic brittleness aside, ceramics are non-metallic, tolerant of high temperatures, extremely strong in compression. As with metal alloys there is an almost infinite number of possible compositions. If one can make a ceramic gun barrel that doesn't explode when a bullet is fired down it, it's your answer.

For fiction, it won't require much suspension of disbelief. If a real ceramic gun barrel does exist, it may be classified information here in the real world.

Note that a ceramic item will be very easily detected by X-rays. Just not by a metal detector that works on electrical conductivity.

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