>3D-printed guns are not a problem that needs solving.

Agree.

>They're mostly dangerous to the user.

Kinda disagree.

Several reasons why:

1) On the AR-15, the lower receiver is the "gun" portion that is serialized. It actually doesn't take too much abuse - you can 3D print one without much difficulty and have a firearm that is not traceable.

2) FDM materials that are basically just enough plastic to bind metal powder in place exist and can be fired in a kiln after being printed on your 3D printer, and you get a metal component.

3) DMLS printers will someday become cheap enough for home use. Patents are starting to expire here, so this will likely happen soon - over the next 10-15 years.

But guns also aren't particularly difficult to build at home with more traditional means either, so I don't think it makes much sense to worry about the 3D printing aspect.

>the lower receiver is the "gun" portion that is serialized.

AFAIK this a problem only under American legislation where the firearm is legally defined by one part, which in AR-15's case happens to be that lower receiver. Here a permit is required for the receiver, barrel, bolt, carrier and all other "substantial" parts, and our gun legislation is relatively lax in comparison to other EU countries.

I'm not European, but from my understanding that's not consistent throughout the EU. In Germany, you can buy receivers—even full-auto ones— over the counter without any sort of license or permit.

Try buying a barrel for an AR-15 in Germany, you'll have to show a WBK (Waffenbesitzkarte).

> you can 3D print [a lower receiver] without much difficulty and have a firearm that is not traceable

I thought it was the barrel that added traceable marks to the bullet, through the rifling?

How does changing the receiver, which does not change the rifling, make it not traceable?

Untraceable in a legal/administrative sense, it could still be traced using forensics.

In the US the lower receiver is the component that is legally considered a firearm. They're required to have serial numbers and are subject to the same laws as a fully functional gun. The other components are just hunks of metal in a legal sense and may be sold and manufactured without restriction. If you are able to fabricate a lower receiver by yourself you can buy the rest of the components you need to assemble a fully functional rifle without any records of its existence or creation.

According to the BATF a block of metal doesn't become a lower receiver until it is more than 80% complete. This led to the creation of a market "80% lowers" that can be legally sold without restriction and completed by the buyer. The hardest milling is done by the manufacturer and they are designed to be completed by inexperienced users with common tools. There's even a company that will sell you a CNC mill preprogrammed to finish milling the receiver.

Probably just in terms of serial number / manufacturer stamp / etc which are what live on the lower.

Well if you're planning to trace weapons by their serial number then you're already going to be defeated by a simple screwdriver, let alone 3D printing.

You'd be surprised how well a serial number can be recovered even after it's been filed away. The stamping process that imprints each digit affects the metal underneath as well. Even when the physical characters have been filed away, the serial is readable using some advanced techniques[1]

[1] https://www.washingtonpost.com/national/health-science/scien...

Bureaucracy is a bigger issue. All guns registered in the US are required by law to have their serial numbers recorded only on paper, not on computers. This means that even if you know the serial number of a gun used in a crime, it can take weeks or months to trace it to a purchaser. The reverse search (find all serial numbers associated with a particular person) is basically impossible.

Source: https://www.gq.com/story/inside-federal-bureau-of-way-too-ma...

Barrels, in the US at least, are trivial to replace.

Easier to make a lower out of cutting boards, wood, or Lego than 3D print one.

The lower isn't universally the serialized part. In some places, it's the barrel.

No it’s not, it might be cheaper but if you have access to a good printer you can’t possibly say that building a lower out of LEGO and cardboard is easier.

Even completing an 80% lower with a dremel tool is harder than loading a file and hitting print.

In my experience, any 3d printed item needs a lot of work to make it functional. It isn't as easy as hitting print and walking away.

Making one with a router and a cutting board is tedious, but I've done it and the result was functional. Making one with Lego and epoxy I have not done, but I know someone that has. It isn't like it takes days.

Depends on the printer with a high end printer you can print a lower and go with no work needed other than to drill the holes for the FCG and magazine and bolt catches.

With a production or industrial prototyping printer you don’t need to do anything than drop your parts in.

Heck it wouldn’t surprise me if in a few years with multi material printing you’ll be able to print a fully functional lower even with the FCG I’ve already seen metal parinting demos that can print both rigid and spring metal materials in the same print.

> On the AR-15, the lower receiver is the "gun" portion that is serialized.

...unless you make your own (or finish a partial one) then you aren't required to stamp it with a serial number or tell any (federal) agency about it, a so called "ghost gun".