Hooooo boy. There’s a lot you can’t do. If you have a rifle (that uses a ‘rifle’ round as opposed to a pistol round), your barrel must be over a certain length. But if you have a “rifle” that is chambered in say 9mm (a pistol round), doesn’t matter. Barrel could be 4 inches long. But then it can’t have a stock. So you have a “wrist brace” (read:totally not a stock I promise) instead. There’s a bunch of wacky shit the atf and congress have come up with.

As someone who studied math in college, but can hardly string a line of code together without making 4 trips to stack exchange or some documentation, this was a very good explanation of why math is actually really exciting.