As Polyglot said you can print a "gun" in the US without needing to make a barrel or other metal parts. So if you are banned from buying a gun, it's still possible to buy all the firing parts and just make the receiver by way of a 3D printer or hammering some sheet metal.

I have seen articles on 3D printers that can print metal parts. I think they are stronger than the plastic parts, but not as strong as cast or forged. But I imagine they would be adequate for many camera related tasks. Basically metal power is applied in layers and a laser fuses powder where the part should be built up. A new layer is added and the process repeats. Very cool stuff.