Again, you can make guns at home, for cheaper than you can buy a complete one in some instances. This mill is literally called the ghost gunner. Fully functional, mil-spec gun parts out of solid metal, no CNC experience needed, in the privacy of your own home. Stopping these machines with thousands of legitimate uses is impossible. They have tried to regulate the plans, but they are already out there...no going back in the tube for that toothpaste.
Ghost Gunner 3-S Deposit - Ghost Gunner
GG3-S allows you to perform common firearms machining operations with confidence and ease, in the privacy of your own home. GG3-S removes material 5 times faster than GG2 and the new unibody construction provides greater rigidity, drastically improving finished part quality. The custom spindle...ghostgunner.net
You could make providing the parts like this illegal.
And again it's not about making it completely impossible. . . it's about making it HARDER.
The right likes to throw out this strawman that essentially states that if a law won't make it IMPOSSIBLE for a person to illegally get ahold of a gun that it won't work. That's not the case. Simply making something harder to do, something that requires more skill, more research, more work, more planning works wonders for reducing these problems.
Enforced Laws work.