As you know, it’s legal in America to build your own standard firearm for personal use [by manufacturing your own receiver.] One of the best ways to get a discreet, legal, off-paper SHTF rifle is an imported de-milled Kalashnikov (AK) kit, with a new, home-built receiver.
Take a look at this web site. His heat treating and machine and tool instructions are accurate. This is the best site I’ve seen on the subject. I was able to tear down a Romanian kit and assemble a working AK in about 8 hours. Beginners will likely need a couple of weekends. – Michael Z. Williamson