Ballistic Fingerprinting’s a Dud: Another failed gun-control strategy.

Ballistic fingerprinting was all the rage just a couple of years ago. Maryland and New York were leading the way where a computer database would record the markings made on the bullets from all new guns. The days of criminals using guns were numbered.

Yet, a recent report by the Maryland State Police's forensic-sciences division shows that the systems in both states have been expensive failures. New York is spending $4 million per year. Maryland has spent a total of $2.6 million, about $60 per gun sold. But in the over four years that the systems have been in effect neither has solved a single crime. To put it bluntly, the program "does not aid in the mission statement of the Department of State Police."

The systems have drained so many resources from other police activities that ballistic fingerprinting could end up actually increasing crime. In New York, how many crimes could 50 additional police officers help solve?

The police explain the program's inability to reduce crime because criminals have simply not been using the guns that have been entered into the database. In some cases the claim is that the wrong data has been entered into the computers.

The physics of ballistic fingerprinting are straightforward enough. 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. In older guns, the bullet's 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 crimes are obtained by the criminal through retail stores or pawn shops. The rest are virtually impossible to trace.

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 few 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 is just another failure in a long line of gun-control measures.

   John Lott Jr, a resident scholar at the American Enterprise Institute in Washington, is author of "More Guns, Less Crime" (University of Chicago Press, 2000) and "The Bias Against Guns" (Regnery, 2003).