There was a panic about plastic guns back in the 80s too when the Glock came out, and Congress passed the Undetectable Firearms Act.

But it was just as misinformed as it is today -- practically speaking, only metal is suitable for the high pressure components of a gun. A common 9mm cartridge produces upwards of 35,000 psi.

Aren't there metals that are undetectable/less detectable, like titanium or even stainless steel?

No, it doesn’t work like that in the modern world. The nature of the materials are pretty obvious to a remotely competent sensor.

using what physical process? How exactly do they detect any metal? A genuine question.

You can detect nonferrous metals by inducing eddy currents in them, then they become magnetic.

> metal detectors are kind of the primary way we try to find guns on people

What are bullets and shell casings made out of again?

More importantly, what is the barrel made out of? Yes, I know there’s some fully printed guns… but my understanding is that those are basically 1-time use and even then it’s questionable how reliable that single use actually is…

If you want something resembling an actual gun (more than one shot, won’t blow up in your hand, some reasonable chance of accuracy, etc), then you’re going to be using multiple metal components (including the bullets of course) all of which would show up on a metal detector.

And I'd argue that shell casings are probably harder to manufacture than a fully working firearm. The equipment needed to manufacture working ammunition end-to-end is pretty serious.

All of these manufacturing equipment and processes existed more than a century ago.

If you have a capable VMC, you can make the die and other equipment necessary to stamp shell casings from commonly-available parts and machinery.

From there, with a modern Dillon or Hornady reloading press, you can crank out thousands of rounds per day without issue.

Primers are a legitimately difficult thing to manufacture, but (good-enough) bullets, casings, etc. are completely doable.

[Primers are a legitimately difficult thing to manufacture]

thats a problem that may not endure. if a firearm is reengineered to use an electrode to detonate charge rather than a chemical primer, there is no need for murcury fulminate, just a piezo electric spark generator, and a few square cm of cerebral cortex.

Electronic primers are a thing that already exists commercially. In the early 2000s, Remington sold electronically primed hunting rifles next to their non-electronic equivalent (see: "EtronX").

It is a mature technology. The main issue is cost and simplicity, since it often requires adding electronics to weapons that normally would not require them. The military uses electronically primed cartridges for things like chain guns and autocannons, since those require electronics to fire regardless of how it is primed.

yes ive seen them they are called exotic by most people around me.

yes the very nature of a chain cannon, makes electronic priming,the easier way to go.

so far we can still go to the store with 20$ and come back with a 200pk of 209s, someday that might be not so easy, and electronic is the better/only way.

What advantage do they have over chemical primers?

It completely eliminates the physics and durability considerations of firing pin design.

For chemical primers there is a non-trivial lag between the trigger breaking and the firing pin being accelerated to sufficient velocity such that it ignites the primer. The mechanics of maximizing acceleration of the firing pin is adversarial to durability, reliability, and precision in a number of respects. In automatic weapons it is made worse because the same physics must run in reverse to support the desired rate of fire.

With electronic primers, you mostly only need to worry about switching electric power fast enough (trivial). The relatively fragile firing pin mechanics don't need to exist. But you do need electronics, which has its own issues.

mechanical parts only move so fast, heat up and wear.

when you have a chain cannon rof 100 rnds per second, it gets intense.

a spark discharge solves a lot of kinetic issues with engineering the mechanism and its timing.

AFAIK, nobody uses fulminate of mercury in primers anymore.

its a good thing too, it not very stable, and mercury is not nice.

but its not difficult to manufacture, if we are in the scenario of shortage or absconderance of products.

lead styphnate is common use, but not everyone is happy with lead either. i have a couple boxes of non lead primers, they smell different when they go off but i havnt encountered noticible difference compared to lead primers.

Yes, those were abandoned a very long time ago. Mercury materially damages steel alloys. Using it in primers slowly eats your barrel.

I have no ability to make primers specifically, and wouldn’t even know where to start.

Imagine a flintlock 3d printed gun with hand cast lead balls: watch out redcoats!

In the movies, you hide the bullets in a pen or something, and it bypasses the metal detector along with the keys, phones and watches.

rabbits' foot, iIrc.

And importantly the barrel. Plastic cannot contain the pressure required to fire a bullet.

> What are bullets and shell casings made out of again?

Usually non-ferrous metals like brass, lead, and copper unless you live closer to Russia, then you may end up with steel-case.

That's besides the point though, the barrel of the gun will be steel.

Ferrous metals aren't required for any modern security-screening metal detectors: these materials are still highly electrically conductive, and therefore easily-detectable eddy currents are still inducible.

Oh, that's right! I remember reading somewhere about this a few years back. Might have even been here on HN.

For some reason I hear "metal detector" and my brain goes right to magnetism.

I don't care how good you are, you cannot 3D print a barrel that will withstand the pressure forces generated by a centerfire round.

Kind of interesting how many of these comments are confidently denying what the 3D printed gun nuts already pulled off 13 years ago. I would never in a million years want to be around one being fired, but there have been big internet communities pulling this off going back a long time https://arstechnica.com/tech-policy/2013/11/feds-get-in-on-3...

If you're dead set on making a gun that will pass through a metal detector you don't need a 3D printer to do it.