Maryland’s long-overdue goodbye to ballistic fingerprinting

Ballistic fingerprinting was all the rage 15 years ago. Maryland led the way, setting up a computer database on new guns and the markings they made on bullets. New York soon followed. The days of criminal gun use were supposedly numbered.

It didn’t work.

The registration of ballistic fingerprints never solved a single crime in Maryland or New York. New York scrapped its program in 2012. This month, Maryland announced it was following suit.

Maryland spent $5 million on its computer database. By 2005, New York was spending about $5 million per year, showing that even greater per-capita spending didn’t guarantee success.

Think of all the other police activities that this money could have funded. How many more police officers could have been hired? How many more crimes solved?

It has long been clear that these states’ programs weren’t working. A 2005 report by the Maryland State Police’s Forensic Sciences Division labeled the operation “ineffective and expensive.” Similar statements by police have been ignored for years.

Gun-control advocates predicted the success of ballistic fingerprinting. For example, Dan Webster of Johns Hopkins’s Bloomberg School of Public Health argued that the vast majority of criminals obtain their guns legally. Authorities, he predicted, would be able to establish matches between firearms in the database and spent rounds found at crime scenes.

Webster was wrong on both counts. Very few criminals legally purchase guns. Recording the markings on guns was a waste of time and money.

But gun-control advocates ignored physics. When a bullet travels through the gun barrel, 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.

Unlike human fingerprints and DNA, a gun’s ballistic fingerprint changes over time because of wear. A child’s fingerprint can still be used much later in life. A ballistic fingerprint, on the other hand, is more like the tread on a car tire. New tires of the same brand and model, with minor exceptions, are essentially identical. Over time, though, friction causes the tread on tires to wear. 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.

The same is true for guns. The greatest friction on a gun occurs when the gun is first fired — and that dramatically and quickly reduces the usefulness of recording the gun’s ballistic fingerprint when it is purchased.

Criminals can thwart ballistic fingerprinting by replacing the barrel of a gun. They can alter the ballistic fingerprint by just scratching the inside of the barrel.

The response from gun-control advocates: Fifteen years and $5 million weren’t enough. They simply need more time because the science is valid. They claim that, on average, most guns used in crimes were bought nearly 15 years prior. But even if that were accurate, it wouldn’t explain why the systems in Maryland and New York haven’t solved one crime.

People should be held accountable for their predictions. The only thing the program accomplished was making it more costly to legally sell guns.

Good intentions don’t necessarily make for good laws. What counts is whether the laws save lives. On that measure, ballistic fingerprinting is just another failure in a long line of failed gun-control measures.

• Lott is the president of the Crime Prevention Research Center and the author of "More Guns, Less Crime" (University of Chicago Press, 2010).