The Montana Firearms Freedom Act, which he drafted and pushed through his state's legislature, declares that guns made in Montana, stamped "Made in Montana" and staying in-state aren't subject to federal regulations.

After the state enacted it, he announced plans to manufacture the Buckaroo, a miniature rifle that is based on an 1899 Winchester model and intended for children between ages five and 10. [Sheesh] Orders, at $200 apiece, poured in. Some came from lawmakers.

"I have four grandkids on the ground, two more on the way, and my youngest gets married on June 12th, so I expect results from him by mid-winter," Republican State Rep. Krayton Kerns told Mr. Marbut by email last year. "Put me down for seven with the option to purchase more."

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives was less enthusiastic. It wrote to Mr. Marbut saying: "Federal law supersedes the [Montana Firearms Freedom] Act, and all provisions of the Gun Control Act and the National Firearms Act" remain in force.

Mr. Marbut went to court. The "Constitution confers no power on Congress to regulate the special rights and activities contemplated by the MFFA," his petition argued, while the Ninth and 10th Amendments assign "all regulatory authority of all such activities within Montana's political borders" to "the sole discretion of the State of Montana."