Home made guns are legal (for the most part) as long as you are making them for yourself.
Until very recently, making a decent gun took a lot of skill, and was pretty dangerous if something wasn't done correctly.
Part of the issue with gun laws is that gun parts, by themselves, are fairly unregulated. You can buy a gun barrel off the Internet with zero paperwork. You can buy optics, grips, springs, pins, etc without any regulations.
So you can print a gun frame, then buy everything else online, and it's all perfectly legal... In most states... If you don't resell, or do anything illegal with it.
The main catch is, if you can legally buy a gun, you can legally make that same gun.
If that gun would be illegal to buy, it's also illegal to make (full auto, suppressed, high capacity, etc.) but the biggest problem is, with the rise of CNC machines, and high quality 3d printing, how would anyone know?
He smoked for nearly 70 years straight, and had emphysema so bad he couldn't leave his house, and had to be on constant oxygen.
He's been on death's door for a few years now.