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By Peter Henderson and Daniel Trotta

SAN FRANCISCO/NEW YORK, Jan 20 (Reuters) - In tracking down illegal weapons, the smoking gun may not be a gun at all.

Bullets are one thing Sacramento Police Detective Greg Halstead can count on to root out weapons that otherwise would be impossible to find. They are also largely missing from the gun control debate in Washington.

Since 2008, California's capital has required ammunition dealers to take names and thumbprints of bullet buyers. They send the information electronically to police computers, which compare the names to an FBI criminal database.

Halstead begins his day looking at a list of buyers, picking out the ones who aren't supposed to own ammunition - or guns. The thumbprint left by each prohibited buyer is nearly perfect evidence of crime.

"The ammunition case is a slam-dunk solid," said Halstead, who regularly turns up illegal guns at homes he otherwise would have no reason to search. Some 154 felony convictions and 92 misdemeanor convictions have resulted so far.

While the gun control initiatives launched by President Barack Obama on Wednesday in response to December's Connecticut school massacre are the most sweeping in decades, they are more focused on guns than bullets and omitted several controls on ammunition that some law enforcement officials say could help.

The United States ended nearly two decades of federal ammunition control in 1986, concluding that regulating bullets was too much effort and failed to improve safety.

Advocates say the major hurdle to effective ammunition control a quarter century ago - laborious cross-referencing of criminal databases - has been made easier by technology.

Even the former head of the Bureau of Alcohol, Tobacco and Firearms, whose 1986 testimony cleared the way for Congress to end ammunition controls, is of two minds now.

Back then, ATF chief Steve Higgins wrote in a memo that was part of the testimony considered by Congress: "Current recordkeeping requirements for ammunition have no substantial law enforcement value."

Speaking to Reuters 27 years later, he saw a chance that some controls on ammunition might work. "It might be like chicken soup - it can't hurt and it might help," he said.

He added that the prime reason ammunition logs lacked any law enforcement value in 1986 was that his agents ignored them. The thinly stretched Bureau of Alcohol, Tobacco and Firearms had 1,829 agents and investigators to police the nation's firearms.

"We were just struggling to get enough people to deal with the gun part of it," Higgins said. "I don't remember doing much in the ammunition area."

Higgins was still skeptical about whether computers would make tracking ammunition purchases easy, but said he was open to the idea.


SHORT LIFE OF A BULLET

Americans buy some 10 billion to 12 billion bullets every year, including military and law enforcement, according to estimates by the industry. Regulating them is a Herculean task but is easier than controlling guns in one significant way: a bullet usually doesn't last long.

While guns are 'durable goods' that can last centuries, bullets last only one shot, and the trail between purchaser and shooter is generally a short one, making it easier to follow.

Ammunition can be regulated in several ways, including recording buyer information; checking backgrounds of would-be buyers; banning Internet sales of ammunition; marking bullets with factory serial numbers or imprints from the gun that fired them; and banning high-capacity magazines.

Of those measures, Obama chose one - asking Congress to reinstate a ban on magazines holding more than 10 rounds.

Only a handful of states regulate ammunition sales in any way: Illinois, Massachusetts and New Jersey. A California law to require logs of some ammunition sales has been stalled in court.

New York last week became the first state to require on-the-spot background checks when buying bullets, and limited magazines to seven rounds. The New York law also requires ammo dealers to register with the state and keep records of purchasers, which will enable police to receive automatic alerts if someone is stockpiling bullets.


BUYING IN BULK

U.S. gun, rifle and ammunition sales to civilians were $4.3 billion in 2011, with bullets amounting to about a third of the total, the National Shooting Sports Foundation estimates.

High-capacity magazines are readily available over the Web - a 33-round magazine for a Glock handgun costs about $50. "You can load up on Monday, shoot until Tuesday," one salesman says in Web video.

Over the years, consumer versions of military rifles have become very popular, and they eat up bullets.

Some 70 percent of ammunition is for non-hunting use, primarily target practice, according to a survey of its members by the National Shooting Sports Foundation.

"The consumption of 1,000 rounds or more is often routine for a weekend trip to the range," the foundation said in a note opposing ammunition regulation.

And while target shooters need to buy in bulk, criminal shootings involve less than four rounds, on average, said Lawrence Keane, the foundation's senior vice president, quoting a 2003 study of Jersey City, New Jersey, police records in the early to mid-90s. (http://link.reuters.com/zub45t)

The study period included years when the federal assault weapons ban was in place, and a 2004 study of the ban by one of the same researchers (http://link.reuters.com/jac45t) was cautious in its conclusion about large-capacity magazine limits. The impact on gun violence from the ban was likely to be small, but guns with large magazines tended to result in more shots fired and more victims.

TRACKING THE BUYERS

Los Angeles has required dealers to log ammunition sales since 1998, and police there say they check logs regularly.

"This is something I think has made L.A. a safer place, really," said Los Angeles Police Department Captain Bill Hart, the head of the gangs and narcotics division.

In California cities that require records of ammunition sales, law enforcement officials have found about 2 percent or 3 percent of sales were to prohibited owners.

Gun rights advocates say ammunition regulations only affect lawful citizens.

"Criminals have other sources of information and would not need to purchase it from California retailers who are required to register their sales," the California Rifle and Pistol Association told the California legislature in a statement submitted to oppose ammunition control.

Keane, of the National Shooting Sports Foundation, argued that Sacramento and Los Angeles have no evidence that crime has decreased because of their laws.

Halstead, the Sacramento detective, acknowledged that one reason for a decrease in prohibited sales in Sacramento could be that illegal buyers were shopping elsewhere.


SERIAL NUMBERS

Northeastern University researcher Glenn Pierce is a co-author of a RAND Corporation study (http://link.reuters.com/byb45t) of Los Angeles ammunition purchase logs from April and May 2004 that found 2.8 percent of purchases were by prohibited possessors.

He sees regulating sales as the first step in ammunition control. The second is to put serial numbers on bullets - one number per box of ammunition. Allowing police to link a bullet to a purchaser would cut the supply of bullets into the illegal market sharply, he argued.

A California bill to put serial numbers on bullets failed in 2005. Ammunition Coding System, a company with a laser-engraving technology for bullets, said the cost would be "not significant" but the industry said it would bankrupt them. The two sides also disagree on whether the serial numbers are always legible.

Another measure proposed in California is to require licenses to buy bullets.


PAST EXPERIENCE

The United States swept in gun control laws after a string of assassinations including those of Martin Luther King Jr. and Robert F. Kennedy. The Gun Control Act of 1968 prohibited mail-order sales of ammunition and required dealers to log their ammunition sales, in part.

The Firearm Owners' Protection Act of 1986, passed under President Ronald Reagan, ended those ammunition regulations and broadly loosened gun control. High-capacity magazines were banned under the 1994 Assault Weapons Ban, which ended in 2004.

Experts consulted by Reuters did not recall any studies of ammunition control in the 1970s and 1980s.

In Washington, little has changed in attitudes towards ammunition control since the memo by then-ATF chief Higgins, even though federal agents cooperate with successful local ammunition programs.

"Our own experience in regulating domestic transfers has shown that there is little utility for law enforcement in imposing the same controls on ammunition transfers as we do on arms. Accordingly, the United States largely eliminated most controls on domestic transfers of ammunition, " Assistant Secretary of State Thomas Countryman was quoted by The Hill as saying on July 10.

That assessment was based on the U.S. experience in 1968-1986 and prepared by the Department of Justice for Countryman, who was negotiating an arms trade treaty.

The White House had no immediate comment on why it did not include more ammunition measures in its package.

Sacramento's Detective Halstead sees his work as extremely relevant to fighting crime. He counts down the list of gang members, parolees, registered sex offenders, and more that his group has tracked down.

"That group represents some people who would have committed some violent crime in our community," the detective concluded. (Editing by Jonathan Weber, Claudia Parsons, Doina Chiacu)

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