MISSOULA, Mont.—With a homemade .22-caliber rifle he calls the Montana Buckaroo, Gary Marbut dreams of taking down the federal regulatory state.

He's not planning to fire his gun. Instead, he wants to sell it, free from federal laws requiring him to record transactions, pay license fees and open his business to government inspectors....

"This is really about states' rights and federal power rather than gun control," Mr. Marbut says. There is "an emerging awareness by the people of America that the federal government has gone too far," he maintains, "and it's dependent on a really weird interpretation."

He is talking about the 1942 Supreme Court case of Wickard v. Filburn, which looms for him the way the Dred Scott decision denying rights to blacks did to antebellum abolitionists....

The narrow question in 1942 was whether the federal government could regulate wheat a farmer grew for use on his own farm. But the constitutional issue concerned how far Congress's authority to oversee interstate commerce stretched....