New technology to link cartridge cases to guns by engraving microscopic codes on firing pins is feasible but did not work equally well for all guns and ammunition in a pilot study by researchers in UC Davis' forensic science program. More testing on a wider range of firearms is needed, the researchers said.
Microstamping technology uses a laser to cut a pattern or code into firing pin heads or other internal surfaces. When the trigger is pulled, the pin hits the cartridge case or primer and stamps the code onto it. In principle, the spent cartridge can then be matched to a specific gun.
Under a law signed by Gov. Schwarzenegger in 2007, all new models of semiautomatic pistols sold in California on or after Jan. 1, 2010, must be engraved in two or more places with identifying codes that are transferred to cartridge cases on firing. Similar legislation has been proposed in other states and at the federal level.
A March 2008 report from the National Research Council, part of the National Academies of Science, described microstamping as a "promising" approach and called for more in-depth studies on the durability of microstamped marks under different firing conditions.
Fred Tulleners, director of UC Davis' forensic science graduate program, and a former state crime lab director, said: "Our study confirms the NRC position that more research should be conducted on this technology."
UC Davis graduate student Michael Beddow tested microstamped marks in one location, the firing pin, in six different brands of semiautomatic handguns, two semiautomatic rifles and a shotgun. The firing pins were engraved with three different types of mark: a letter-number code on the face of the firing pin, a pattern of dots or gears around the pin, and a radial bar code down the side of the pin.
Beddow fitted engraved firing pins into six Smith and Wesson .40-caliber handguns that California Highway Patrol cadets used for training. After firing about 2,500 rounds, the letter-number codes on the pin faces were still legible, with some signs of wear. But the bar codes and dot codes around the pin edges were badly worn.
Tests on other guns, including .22-, .380- and .40-caliber handguns, two semiautomatic rifles and a pump-action shotgun, showed a wide range of results depending on the weapon, ammunition and type of code, Beddow found. Generally, the letter-number codes on the firing pin faces transferred well to cartridge cases, and so did gear codes, while the bar codes on firing pin sides performed more poorly. Microstamping worked particularly poorly for the one rimfire handgun tested.
Codes engraved on the firing pin faces could be removed easily with household tools, Beddow found.
The new California law requires at least one other internal microstamp; this study did not test anything but the firing pin. Based on the study's preliminary results with a .22-caliber pistol, where the code on the firing pin was transferred to the brass of the cartridge rather than the softer primer, the effectiveness of such a requirement needs further assessment, Tulleners said.
David Howitt, professor of chemical engineering and materials science at UC Davis, supervised the project.
The study was funded by a grant from the California Policy Research Center, part of the UC Office of the President. The report has completed peer review by experts selected by the center, and a paper describing the results has been accepted and scheduled for publication in an upcoming issue of the Association of Firearm and Toolmark Examiners Journal.