Bullets and Bunkum
The futility of 'ballistic fingerprinting.'

In the wake of the Washington, D.C., sniper attacks, many are viewing ballistic fingerprinting as a magic crime-solving tool. According to the pro-gun-control Brady Campaign, such a system "would have solved [the sniper case] after the first shooting"; a Washington Post columnist calls it a "common-sense measure"; and many politicians are jumping on board, including New York Democratic senator Charles Schumer and Maryland Democratic gubernatorial nominee Kathleen Kennedy Townsend. Unfortunately, the issue is not so simple: By draining resources away from other police activities and making it costly for law-abiding citizens to own guns, ballistic fingerprinting could end up actually increasing crime.

The physics of ballistic fingerprinting are straightforward. When a bullet travels through the barrel of a gun, the friction creates markings on the bullet. If the gun is new, imperfections in the way the barrel is drilled can produce different markings on the bullet; such imperfections are most noticeable in inexpensive guns. (This poses an irony for gun controllers, who push for laws that ban inexpensive guns.) In older guns, the bullets' friction through the barrel can cause more noticeable wear marks that help differentiate between guns. Many other factors influence the particular markings left on the bullets - for instance, how often the gun is cleaned and what brand of cartridge is used.

Precisely because friction causes wear, a gun's ballistic fingerprint changes over time - making it drastically different from such forensic evidence as human fingerprints or DNA. The recording of a child's fingerprints or DNA still allows for identification much later in life; the same is not true of the bullet markings. A ballistic fingerprint is less like a human fingerprint than it is like the tread on a car tire.

Brand-new tires are essentially identical, so new-tire tracks at crime scenes leave investigators with pretty limited information. Unless there happens to be a particular imperfection, only the brand and model of the tire can be identified. Imprints on bullets are similar. When a bullet is fired from a new gun, investigators can typically identify only the type of ammunition and the type of gun. Over time, though, friction causes the tread on tires to wear. It would be easy to take the tire tracks left at a crime scene and match them with a suspected criminal's car; but the more the car is driven after the crime, the harder it is to match the tire tracks left at the scene to the tires when they are eventually found. Similarly, the greatest friction on a gun occurs when the gun is first fired - and that dramatically reduces the usefulness of recording the gun's ballistic fingerprint when it is purchased.

Moreover, ballistic fingerprinting can be thwarted by replacing the gun's barrel - just as criminals can foil tire-matching by simply replacing their tires. In general, the markings on bullets can be altered even more quickly and easily than the tread marks on tires: Scratching part of the inside of a barrel with a nail file would alter the bullet's path down the barrel and thus change the markings. So would putting toothpaste on a bullet before firing it.

Ballistic fingerprinting faces other difficulties. For example, even if the gun was not used much between the time the ballistic fingerprint was originally recorded and the time the crime occurred, police still have to be able to trace the gun from the original owner to the criminal - but only 12 percent of guns used in crime are obtained by the criminal through retail stores or pawn shops. The rest are virtually impossible to trace.

So far only Maryland and New York have started recording the ballistic fingerprints of all new handguns sold. While Maryland's program technically started in January 2001, the cost of implementing the program made it unprofitable for gun makers to sell handguns in the state for the first six months of that year. The state government faced a $1.1 million start-up cost and another $750,000-a-year operating cost. New York's program began in March 2001, with a state start-up expenditure of about $4.5 million. (No estimates are available yet on New York's annual cost.)

In both states, the costs for dealers, gun makers, and prospective gun owners were responsible for reducing handgun sales to law-abiding citizens. And what was the specific benefit? Almost zero. The programs have not helped solve a single violent crime in either state; they have so far been used only to identify two handguns stolen from a Maryland gun shop.

A recent study by the State of California points to further practical difficulties with ballistic fingerprinting. The study tested 790 pistols firing a total of 2,000 rounds. When the cartridges used with a particular gun came from the same manufacturer, computer matching failed 38 percent of the time. When the cartridges came from different manufacturers, the failure rate rose to 62 percent. And this study does not even begin to address problems caused by wear, so the real-world failure rate can be expected to be much higher. The California report warned that "firearms that generate markings on cartridge casings can change with use and can also be readily altered by the users." Further, it warned that the problems of matching would soar dramatically if more guns were included in the sample. The study's verdict: "Computer-matching systems do not provide conclusive results . . . potential candidates [for a match must] be manually reviewed."

While registering guns by their ballistic fingerprints is a relatively new concept, we have had plenty of experience using gun registration in general, and it has come up woefully short. A couple of years ago, I testified before the Hawaii state legislature on a bill to change registration requirements. Hawaii has had both registration and licensing of guns for several decades.

In theory, if a gun is left at the crime scene, licensing and registration will allow the gun to be traced back to its owner. Police have probably spent hundreds of thousands of man-hours administering these laws in Hawaii. But despite this massive effort, there has not been a single case in which police claimed that licensing and registration have been instrumental in identifying a criminal.

The reason is simple. First, criminals very rarely leave their guns at a crime scene, and when they do, it is because the criminals have been killed or seriously wounded. Second - and more important for ballistic fingerprinting - would-be criminals also virtually never get licenses or register their weapons. The guns that are recovered at the scene are not registered.

Good intentions don't necessarily make good laws. What counts is whether the laws actually work, and end up saving lives. On that measure, ballistic fingerprinting - a useless diversion of valuable police resources - fails conspicuously, and it should be opposed by anyone who wants to live in a safer society.

Mr. Lott, a resident scholar at the American Enterprise Institute, is the author of More Guns, Less Crime.