If a ban is passed the manufacture of 30-round magazines will be just as illegal as owning one. And the penalties are often far worse! To the tune of thousands of dollars and up to 10 years in federal prison. That's the way that it is now for machine guns and other NFA devices, and the way that it was during the previous ban.
I *could* grow pot and poppies and cocoa plants in my backyard with the intent of manufacturing drugs. This doesn't make it any more legal under current federal law, even if it's only for my own personal use. Still get to go to prison when I get caught.
You will have many recoverable tape errors.