I think they are responding to the OP’s comment:

and would also potentially be somewhere between a misdemeanor and a felony depending on where you are in the US, as 3d printed firearms are generally without serial numbers and are thus ‘ghost guns’, which are often illegal if unregistered, if not outright banned, though this differs from state to state and city to city.

Which has nothing to do with NZ.

Edit: that last bit sounded catty; not my intention.

I would ask your lawyer before investing in the infrastructure.

Many of the US’ gun laws come down to “intent”. Almost like they were written from the start to be selectively enforced.

However, selling them without a serial number is illegal.

That’s not correct either . Federally it is legal to sell a self built firearm with no serial number as long as you did not originally build it with the intention of selling.

Now with Trump admin approved scripts!