Read the statutes, and the case law. Text of U.S. federal switchblade act, including notes and cross-references Raw text from a law school website. People make them. Complying with the law, circa 1866.
Truth is definitely stranger than fiction.
This page created and maintained by a British collector. My good friend Keith Spencer runs this. I had to write them all down, because there were too many to remember. I still don't know. The 4th edition is the latest legitimate edition.