Hardy also earlier wrote a scholarly article on the FOPA, which can be found here: THE FIREARMS OWNERS' PROTECTION ACT: A HISTORICAL AND LEGAL PERSPECTIVE
It contains an editor's note that lists a number of SCOTUS and lower level cases that have cited this article.
The legislative history is here: http://www.firearmslaw.info/FOPA
The first para at the site:
A large portion of what we today regard as the Gun Control Act of 1968 -- and virtually all of its safeguards and protections -- derives, not from the legislation of 1968, but from the amendments known as the Firearm Owners' Protection Act, pushed in the House by Rep. Harold Volkmer, and in the Senate by Sen. James McClure. That statute extensively rewrote the earlier law, expressly overruled six Supreme Court decisions construing it, and negated about a third of the case law which had arisen under it. For an extensive discussion of the statute, see my article, The Firearm Owners' Protection Act: A Historical and Legal Analysis, 17 Cumb. L. Rev. 585 (1986), online here.