Since Congress enacted the federal assault weapons ban, the use of assault weapons in crimes has gone down, but criminal use of guns with large capacity magazines has remained steady or increased, according to a new report from the University of Pennsylvania's Jerry Lee Center of Criminology.

The National Institute of Justice-sponsored report, written by Lee Center research associate Christopher Koper, examines the ban's success in reducing gun violence with assault weapons and guns equipped with large ammunition magazines.  It is the latest in a series of reports and articles on the federal assault weapons ban, including a 1997 report for Congress, written by Koper and Jeffrey Roth, associate director of the Lee Center.

The federal ban, due to expire Sept. 13 unless reauthorized by Congress, prohibits semiautomatic firearms with multiple military-style features and also bans ammunition magazines holding more than 10 rounds; however, the ban exempts millions of assault weapons and large capacity magazines that were manufactured prior to Sept. 13, 1994.  The report stresses the importance of the magazine ban, noting that, while assault weapons were used in about 2 percent of gun crimes prior to the ban, guns equipped with large magazines including the banned assault weapons and other non-banned guns were used in as many as 25 percent of gun crimes.

Analyzing national data and data from several cities, such as Baltimore, Miami and Milwaukee, Penn researchers found that assault weapons, though rarely used in crimes before the ban, typically declined by a third or more as a share of guns recovered by police in criminal investigations during the post-ban period of 1995-2003; however, this decline was offset through at least the late 1990s by steady or rising use of other guns equipped with large magazines.    

"Although assault weapons are used in crime less frequently than before the ban, criminal use of guns with large magazines has not yet declined, in part because exemptions in the law have allowed continued importation of millions of pre-ban magazines to enhance the already large domestic stock," Koper said.  

"Evidence suggests that extending the ban might produce a small reduction in shooting deaths and injuries by reducing attacks with high numbers of shots fired; however, this won't be evident until the stock of large capacity magazines available to criminals is diminished, and that could still take a while," Koper added.

The report indicates that restricting the flow of large capacity magazines into the country from abroad may be necessary to achieve the desired effects from the ban, particularly in the near future.  But it questions whether mandating further design changes in the outward features of semiautomatic weapons, such as removing all military-style features, will produce measurable benefits beyond those of restricting ammunition capacity.  

The report assesses how the ban's reauthorization or expiration might affect future trends in gun violence, concluding that, if the ban is lifted, gun and magazine manufacturers may reintroduce assault weapons models and large caliber magazines, perhaps in substantial numbers.  

In addition, pre-ban assault weapons may lose value and novelty, prompting some of their owners to sell them in undocumented secondhand markets where they can more easily reach high-risk users, such as criminals, terrorists and other potential mass murderers.