I really don't see 3D-printed firearms as a threat. It requires expensive, specialized equipment and days of patience to produce a product that is almost universally inferior to a length of pipe, a block of wood, and a nail. Everything one needs to create an improvised firearm is available cheaper and with less scrutiny at the hardware store.
Despite all the fight over distributing models for this junk, Defense Distributed also currently sells a genuinely dangerous CNC product[0] that is designed to automatically mill out so-called 80% receivers.
If you're not familiar with U.S. firearm law, the part of a gun that's legally considered a "firearm" is the frame or "receiver" that houses the other components. If you sell or produce one of these frames, you are selling or producing a firearm, whether it's made of plastic or metal. Companies get around this by selling incomplete receivers that still require machining, and Defense Distributed sells everything you need to finish the receiver and commit the felony yourself.
I don't actually know if there's actually any evidence of crimes (beyond production) committed with completed receivers but what I do know is that it has much more potential to create an actually reliable and dangerous firearm than 3D printing.
You can finish an AR-15 80% lower with commonly available hand tools in a few minutes. I don't see how the CNC machine that automates this procedure is somehow "dangerous". It's just a smaller, cheaper, and more specialized variant of a regular CNC machine which anyone could already buy.
You're 100% correct-- I believe it's more legally dangerous to those purchasing it than physically dangerous. It just lowers the barrier of entry and creates a frictionless path where someone buys a bunch of products, combines them in the way they were intended and they commit a felony and get a reliable firearm. When combined with the rhetoric that doing so is patriotic or in support of your rights it becomes worrying.
It sounds more frictioned if anything. Both would be pretty simple detective work. "Shooter had gun and ammo. Shooter bought from Bob's Guns. Case closed." vs "Shooter purchased receiver, ghost gunner, guncotton, loading bench, cases and primers, and prefabricated bullets/lead and casts. Case closed."
Also ability to get ammunition. Black powder is easy to make but it's dirty and modern smokeless powder is more difficult. Never mind percussion caps. Without ammunition guns aren't much good, no matter how they are made.
There are a couple fairly recent designs for 3D printed guns that are useful weapons, certainly better than the pipe-wood-and-nail arrangement. For example, the Washbear PM522 and the Liberator 12K shotgun.
But as another poster pointed out, ammunition is a completely different matter and is really the gating factor in all of this.
You're right, I was hyperbolizing somewhat, and I honestly hadn't looked into either of those designs closely before. The Liberator12K looks like it uses a steel barrel, which makes sense. I'm surprised the PM522 works as well as it does but I guess if any fully plastic design is going to work halfway decently, it would be a .22 Revolver.
Despite all the fight over distributing models for this junk, Defense Distributed also currently sells a genuinely dangerous CNC product[0] that is designed to automatically mill out so-called 80% receivers.
If you're not familiar with U.S. firearm law, the part of a gun that's legally considered a "firearm" is the frame or "receiver" that houses the other components. If you sell or produce one of these frames, you are selling or producing a firearm, whether it's made of plastic or metal. Companies get around this by selling incomplete receivers that still require machining, and Defense Distributed sells everything you need to finish the receiver and commit the felony yourself.
I don't actually know if there's actually any evidence of crimes (beyond production) committed with completed receivers but what I do know is that it has much more potential to create an actually reliable and dangerous firearm than 3D printing.
[0]: https://ghostgunner.net/