Why do none of these posts account for the enormous admin time of tracking every minute of your life?

Yeah, that's fair. But I'd point out what makes a firearm a firearm isn't it being shaped like a firearm. It is the ability to detonate the firing cap of standard ammunition in a contained space with trapped expanding gas behind it. Those components can likely be found in their functions in combination (and probably shape - a gun won't work unless the barrel is exact to standard ammunition sizes.

I reckon you can define a gun for pattern recognition. It must have a mechanism to propel a firing pin for standard ammunition, and it must have a chamber to hold a round, of standard ammunition. It likely needs at least some form of barrel to contain the gas and enable acceleration.

And pattern recognition does not have be to software, you can hard code it into the device.

It doesn't need to be perfect, just a PITA to get around.

From a public policy perspective, this could be relatively easy. "3D printers that can be used to manufacture firearms are illegal." Engineers will quickly figure out the rest.

No, this can be done under standards and failsafes. Almost all commercially available printers and photocopires will blank refuse to make a copy of a banknote, for example.

Is it 100% effective? No.

But just like the security of money is based on the principle of it just has to cost more to counterfeit than the face value of the note; for guns, it just needs safeguards to make it more difficult to print illegally a weapon, than illegally source one.