Editor's note: Philip J. Cook is ITT / Terry Sanford Professor of Public Policy at Duke University. Jens Ludwig is the McCormick Foundation Professor of Social Service Administration, Law and Public Policy at the University of Chicago. Cook and Ludwig are co-editors (with Justin McCrary) of Controlling Crime: Strategies and Tradeoffs (forthcoming, University of Chicago Press).

(CNN) -- The assassination attempt and mass killing in Tucson, Arizona, last Saturday was reportedly committed with a Glock 9 mm semiautomatic handgun equipped with a high-capacity magazine that held 31 bullets.

The shock of having a member of Congress shot in the head at close range has led many Americans to wonder: Was it a mistake in 2004 for Congress to sunset the assault weapons ban, which, among other things, banned the manufacture or import of new magazines holding more than 10 rounds? Is it a mistake for America to have such weak firearm regulations more generally?

Congress let the 10-year-old assault weapons ban expire in 2004, and the only notable gun-related legislation under President Obama has been to legalize concealed carrying in national parks. Most of the "action" around gun regulation is in the courts, where "gun rights" advocates seek to tear down regulations under the banner of an extreme laissez-faire interpretation of the Second Amendment.

Democratic politicians have backed off of this issue or, like the Tucson victim, Rep. Giffords, have endorsed gun carrying. The tragedy in Tucson seems unlikely to stimulate much sustained political support for major new gun regulations, given how quickly public interest in this issue faded out after other mass shootings.

A small sampling of these notorious cases helps demonstrate the point: Killeen, Texas; the Long Island Railroad; Jonesboro, Arkansas; Columbine High School; Red Lake High School; Trolley Square Mall; Northern Illinois University; Virginia Tech; Binghamton, New York; and, last August, in Lake Havasu City, Arizona (five of the six victims dead).

Still, perhaps there is now a chance for Congress, faced with this attack on one of their own, to take modest steps to reduce the ease with which psychotic individuals can shoot large numbers of victims. One such step is to reinstate the prohibition on high-capacity magazines.

What good would such a ban accomplish? In the case of Tucson, news reports indicated that the shooter was subdued by private citizens while he was trying to reload his weapon. Had his magazine held fewer rounds, he would have had to reload sooner than he did, and perhaps fewer people would have died as a result.

More generally, research by Christopher Koper of the Police Executive Research Forum suggests that on average, only one in every three or four shots fired by criminal assailants winds up hitting someone. Having a high-capacity magazine enables criminals to fire more rounds more quickly; all else equal, more shots fired means more victims shot.

A high-capacity magazine in effect turns a semiautomatic firearm into a weapon of mass destruction. The public interest in getting such weapons off the street was recognized by Congress back in 1934, when, with the support of President Franklin Delano Roosevelt and FBI Director J. Edgar Hoover, the National Firearms Act was enacted. It effectively stopped commerce in machine guns of the sort wielded to such deadly effect by John Dillinger, Pretty Boy Floyd and the employees of Murder Inc.

Banning high-capacity magazines is a modest, incremental step that would achieve modest benefits. Research by Koper and others shows that in the majority of gun homicides in the U.S., only a few shots are fired. Only about 3% of all criminal homicides involve multiple killings. But as Tucson tragically reminds us, mass shootings have a vastly disproportionate impact on our sense of well-being and security.

Incidentally, it is important that this time the ban go further than the 1994 assault weapons ban. That law had a giant loophole -- it grandfathered all existing large-capacity magazines, and there were millions in circulation at the time in the United States (or that could be imported from Eastern Europe). This time, we would hope for a flat ban on transfer or possession, such as the one that exists, say, in New York state.

As economists, we take seriously the importance of comparing benefits to costs of any new policy, and we recognize that many people wish to keep guns for legitimate uses like self-defense and hunting. Fortunately, the costs of banning high-capacity magazines also seem to be extremely modest.

Author John Lott, an economist who supports gun carrying, says that in the vast majority of cases in which a private citizen uses a gun in self-defense, the gun is only brandished and not actually fired at the assailant. Banning high-capacity magazines will have a negligible effect on the ability of citizens to use guns to protect home and hearth. For hunters, a ban on high-capacity magazines would be largely irrelevant.

More dramatic changes in federal gun laws might have greater effects on public safety but seem unlikely in the current political climate. Banning high-capacity magazines strikes us as a common-sense policy change that is likely to generate modest but important benefits to society at a very small cost, and so is worth doing.

The opinions expressed in this commentary are solely those of Philip Cook and Jens Ludwig.