An anti-government activist from Montana who prosecutors say sought out high-powered weaponry for an anticipated "second American Revolution" was sentenced to six years in prison Thursday.

William Krisstofer Wolf advocated a "shocking" level of violence against law enforcement and others, U.S. District Judge Susan Watters said in court.

The Gallatin County man was arrested last year after buying an illegal, fully-automatic sawed-off shotgun from an undercover FBI agent for $725 in the parking lot of a truck stop. He was convicted on federal weapons charges in November.

Authorities say Wolf compared shooting police to hunting gophers and spoke of dropping napalm on the county courthouse.

He vowed to appeal, claiming the shotgun was for self-defense and that his extreme views were constitutionally protected free speech. Prosecutors had asked for a 10-year sentence, almost double what is recommended under federal sentencing guidelines.

The judge said Wolf's statements revealed his intentions for violence.

An automatic shotgun is categorized as a machine gun under federal law and can be bought only with a special permit, which Wolf did not have. Shotguns with shortened barrels also are illegal.

Assistant U.S. Attorney Bryan Whittaker said stiff a prison sentence was needed to deter Wolf and send a message to others who might contemplate violence against the government.

"Wolf made law enforcement and judicial officers his targets," Whittaker wrote in documents submitted to the court. "Wolf remains undeterred. A significant sentence is needed to address his contempt for the law."

On his webcast, Wolf proposed citizen arrests of judges by militia-like safety committees. He testified at trial that he also wanted to acquire a flamethrower, which is allowed under federal law.

Wolf's attorney, Mark Werner with the Federal Defenders Office, objected to the prosecutions' assertions and asked for a sentence of 27 to 33 months. His client has no history of violence and did not intend to use the shotgun on any particular person, Werner said.

Wolf "felt a war was coming much like the Revolutionary War fought to remove the oppression of the British government," Werner wrote. "There was no evidence presented that he threatened public officials. He didn't like some of them. He thought some were corrupt. But he didn't threaten to kill."

The Associated Press contributed to this report.