From that perspective, any machine or tool will have to be rendered obsolete, and frankly, that includes everything, starting from basic machine tooling to a blacksmith's hammer or a casting mold. This phenomenon is called "dual use", and if it gets too common, it just loses it's purpose. Also, restricting certain products will only cause market to figure out a method around it.

Pressure-bearing parts are not 3D printed, never, unless you've got a laser sintering machine at your disposal, which currently cost +100k and beyond, and the materials, planetary ball milled metallic powders, that ignite upon contact with atmospheric oxygen, cost $300/kg and above.

Also, there are countless items that share similar mechanisms. If you know gun mechanics, you know how universal shapes those are. For common people, you only need 1-2 seconds with a gun to disassemble it into two or more parts to make it unrecognizable as a firearm to most of them, and that's only with guns that look like guns.

This is not black and white scenario. This is a scenario with technology that supports other technologies. While making pressure bearing parts from metal is easy-ish with basic machine tooling, frames, receivers, grips, stocks and many secondary parts isn't - but then you can 3D print them. Now you have a gun that has all important - but simple - parts made out of high strength alloys, but all secondary parts 3D printed.

This terms me you know nothing about CAD, 3d printing, or firearms.

The 3d printed part is not usually the pressure holding part, and is not distinguishable from, say, a custom nerf gun part or a whole host of other things you can’t even think up as an individual. There would either be so many false positives in a hypothetical AI gun detector that the software would be unusable, or it would do nothing.

There’s entire 3D printed model guns that do not function outside of being a novelty toy. You want to attempt to ban that as well?