[qnzhouka] How to create illegal goods

What censorship mechanisms are in place to prevent people from making a good for themselves that is illegal to buy publicly?

Inspired by the furor over 3D printing a gun.  However, if you want to make a gun with rapid prototyping, a CNC mill is probably a better way to go, since it can easily mill metal instead of printing a plastic one which can fire at most once.

How difficult is it to mill a fully automatic weapon? Are designs available?  I speculate the AK-47 does not require very precise manufacturing tolerances, which speaks to Kalashnikov's design skill.  One imagines a vendor who rents out a CNC mill and doesn't ask questions.

Stopping the flow of information is more difficult than, or at least, very different from, stopping the flow of goods.