B. Todd Jones's unexpected resignation as head of the Bureau of Alcohol, Tobacco and Firearms Friday closely follows a controversial attempt by ATF to implement new rules for judging ammunition.

The ATF announced that Jones, Minnesota's former U.S... Attorney, would leave just 19 months after his confirmation "to pursue opportunities in the private sector." His resignation, effective March 31, comes a month after the proposed ammunition rules blew up in a fury of protests from gun rights groups.

The National Rifle Association flexed its political muscles strongly as thousands of angry letters poured into the ATF. But most telling might have been letters in early March signed by dozens of U.S... Senators and 237 U.S... Representatives, including Democrats Collin Peterson and Tim Walz and Republicans John Kline, Tom Emmer and Erik Paulsen of Minnesota.

The gun rights lobby objected to the rules that the ATF wanted to apply to determine the kinds of ammunition used primarily for sporting purposes. The rules might have excluded some armor-piercing bullets from the market. Critics of the policy, including the members of Congress, complained that  the standard was "unduly restrictive," could undermine the Second Amendment and disrupt the market for ammunition used for legal purposes.

"The opposition to the ammo is typical of the firestorm that agency can generate," said University of Richmond law professor Carl Tobias. "Maybe that was the final straw [for Jones]. That's the kind of conclusion you would draw."

Tobias, like most, was surprised by Jones' departure because he had survived sometimes scathing confirmation hearings.  

Jones took over the ATF in the wake of the "Fast and Furious" scandal in which the agency failed to properly track weapons purchased along the nation's Southwest border. The weapons sometimes ended up in the hands of criminals and in one case an untracked gun was used to kill a U.S... Border Patrol agent.

Tobias, who specializes in federal matter, felt Jones was doing a good job.

"We didn't hear much about the agency," he said. "That, to me, is a sign things were getting better."