Re: Ah, you need to read up, Lewis
the aforementioned "ghost gun" lower is legally an 80 percent receiver and is totally legal to mail as it is not "yet" a firearm.
It does not require CNC to complete. A $75 reusable jig, a trim router, a 3/8 chuck hand drill,some drill and cutting bits, and a decent bench with clamps and you're done. I finished one just for the hell of it three weeks ago and helped a buddy do his last weekend. Takes less than a workday. And still perfectly legal even in California, USA.
Biggest reason I built one and will do another? Because it costs less. The 80 percent lower is still cheaper than getting one shipped to CA and all the legal paperwork, waiting periods, two trips to the FFL/dealer (one to sign for receipt, another after 2 week waiting period), and legislative paperwork needed to remain in compliance. Even counting cleaning up a huge mess of aluminum shavings in the garage as time spent, I still come out on the positive side.
Plus I p*ssed off a legislative type who refuses to realize that the crooks aren't gonna go thru the hassle, and get better stuff cheaper and with no work along with the tons of drugs and humans the coyotes bring across.
P.S. This still does not make, nor even come close, to creating an "assault rifle". The internal parts for fire control (which for standard AR's are a bunch of springs and pins also mail-order capable) are not part of an 80 percent build and beyond the scope of anyone without a really good CNC system. The parts kits cannot be modified for select fire as their configuration shares almost nothing other than trigger and maybe the hammer. Disconnector, fire control selector, and a bunch else are completely different. It's like saying a Mini can be made into a 10 second quarter miler with just a few parts, one of those parts being an entire 500 cubic inch supercharged V8, and the others being a whole new fuel cell system and completely different frame.