A Colt AR-15, now legal with a bayonet mount, flash suppressor, collapsible stock and a high capacity magazine that holds more than 30 rounds. (Thomas Cooper/GETTY IMAGES)

During the 10-year federal ban on assault weapons, the percentage of firearms equipped with high-capacity magazines seized by police agencies in Virginia dropped, only to rise sharply once the restrictions were lifted in 2004, according to an analysis by The Washington Post.

The White House is leading a push to reinstate a national ban on large-capacity magazines and assault weapons after a gunman armed with an AR-15 and 30-round magazines killed 20 children and seven adults in Connecticut. Vice President Biden has been holding advisory meetings to hammer out a course of action that will address the issue of the larger magazines, which under the lapsed federal ban were those that held 11 or more rounds of ammunition.

In Virginia, The Post found that the rate at which police recovered firearms with high-capacity magazines — mostly handguns and, to a smaller extent, rifles — began to drop around 1998, four years into the ban. It hit a low of 9 percent of the total number of guns recovered the year the ban expired, 2004.

The next year, the rate began to climb and continued to rise in subsequent years, reaching 20 percent in 2010, according to the analysis of a little-known Virginia database of guns recovered by police. In the period The Post studied, police in Virginia recovered more than 100,000 firearms, more than 14,000 of which had high-capacity magazines.

Researchers see impact

To some researchers, the snapshot in Virginia suggests that the federal ban may have started to curb the widespread availability of the larger magazines.

The number of high-capacity magazines seized by Virginia police decreased during the federal assault weapons ban.

“I was skeptical that the ban would be effective, and I was wrong,” said Garen Wintemute, head of the Violence Prevention Research Program at the University of California at Davis School of Medicine. The database analysis offers “about as clear an example as we could ask for of evidence that the ban was working.”

The analysis is based on an examination of the Criminal Firearms Clearinghouse, a database obtained from state police under Virginia’s public information law. The data, which were first studied by The Post in 2011, offer a rare glimpse into the size of the magazines of guns seized during criminal investigations. The Bureau of Alcohol, Tobacco, Firearms and Explosives, which traces guns and regulates the industry, tracks details about the guns seized after crimes but not the magazine size.

The initial Post analysis was prompted by a mass shooting in Tucson. Jared Lee Loughner — armed with a legally purchased 9mm semiautomatic handgun and a 33-round magazine — opened fire outside a grocery store, killing six people and wounding 13, including Rep. Gabrielle Giffords (D-Ariz.).

In the following two years, a succession of mass shootings has occurred, including several in which the gunmen reportedly had high-capacity magazines.

At the Dec. 14 shooting in Newtown, Conn., the gunman was reported to have been armed with two handguns, an AR-15 rifle and numerous 30-round magazines. He killed himself at the scene. The guns were legally purchased by his mother.

The federal ban that expired in 2004 prohibited the manufacture of magazines capable of holding more than 10 rounds. But the law permitted the sale of magazines manufactured before the ban. By some estimates, 25 million of the large-capacity magazines were still on the market in 1995.

Many semiautomatic rifles and semiautomatic handguns accept magazines of various sizes. Larger magazines increase a gun’s firepower, enabling more shots before reloading.

The Virginia database analyzed by The Post lists about three-quarters of guns recovered by police, missing the rest because some agencies failed to report their recoveries to the state. The database contains details about more than 100,000 guns recovered by 200 police departments in a wide range of investigations from 1993 through August 2010, when The Post last obtained it.

In recent weeks, The Post conducted additional analysis into the type of guns confiscated with large-capacity magazines. The guns included Glock and TEC-9 handguns and Bushmaster rifles. Most had magazines ranging from 11 to 30 rounds.

Of 14,478 guns equipped with large-capacity magazines that were confiscated by police, more than 87 percent — 12,664 — were classified as semiautomatic pistols. The remainder were mostly semiautomatic rifles.

The Post also identified and excluded from the counts more than 1,000 .22-caliber rifles with large-capacity tubular magazines, which were not subject to the ban.

In Virginia, handguns outfitted with large-capacity magazines saw the biggest fluctuation during and after the ban.

In 1997, three years into the ban, police across the state reported seizing 944 handguns with large-capacity magazines. In 2004, the year the ban ended, they confiscated 452. In 2009, the last full year for which data were available, the number had rebounded to 986 handguns, analysis showed.

Of these, the single biggest group were handguns equipped with 15-round magazines, accounting overall for 4,270 firearms over the 18 years.

Effect hard to measure

Nationwide, researchers who studied the federal ban had difficulty determining its effect, in part because weapons and magazines manufactured before the ban could still be sold and in part because most criminals do not use assault weapons.

Christopher Koper, who studied the ban’s effect for the National Institute of Justice, the research arm of the Justice Department, noted in a 2004 report that the “success in reducing criminal use of the banned guns and magazines has been mixed.”

He found that gun crimes involving assault weapons declined between 17 and 72 percent in the six cities covered in the study — Anchorage, Baltimore, Boston, Miami, Milwaukee and St. Louis. But he said he found no decline in crimes committed with other guns with large-capacity magazines, most likely “due to the immense stock of exempted pre-ban magazines.”

Koper’s study tracked guns through 2003. He said that The Post’s findings, which looked at magazine capacity of guns recovered in Virginia before and after 2003, suggests that “maybe the federal ban was finally starting to make a dent in the market by the time it ended.”

Koper, now an associate professor of criminology at George Mason University, also noted the ban on high-capacity magazines might improve public safety because larger magazines enable shooters to inflict more damage.

The use of high-capacity magazines is a contentious point in the gun debate.

“Anyone who’s thought seriously about armed self-defense knows why honest Americans — private citizens and police alike — choose magazines that hold more than 10 rounds. Quite simply, they improve good people’s odds in defensive situations,” Chris W. Cox, the executive director of the National Rifle Association’s legislative institute wrote in a piece posted online. He called the ban a “dismal failure.”

The federal prohibition on ­high-capacity magazines and assault weapons was spurred in part by the 1989 mass killing in Stockton, Calif. Patrick Edward Purdy, a mentally unbalanced drug addict, fired 110 rounds from an AK-47 into a schoolyard, killing five children and wounding 29 others and a teacher. Purdy used a 75-round drum magazine and a 35-round banana clip, one of four he carried.

Some states still limit magazine size. Maryland limits the size to 20 rounds; California limits it to 10. Connecticut, the location of Sandy Hook Elementary School, does not.

After Giffords’s shooting, Rep. Carolyn McCarthy (N.Y.) and other Democrats proposed legislation to ban the sale or transfer of high-capacity magazines. McCarthy’s husband and five others were killed in 1993 on the Long Island Rail Road by a gunman armed with a semiautomatic pistol and four 15-round magazines. He fired 30 shots before being subdued as he swapped magazines.

In the wake of the Newtown shooting, President Obama and lawmakers urged that a ban on assault weapons and high-capacity magazines be made permanent.

The NRA and the National Shooting Sports Foundation, a gun industry group, have historically opposed any restrictions on magazine capacity. The NRA did not respond to requests for comment, and the sports foundation declined to comment.