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.
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