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Shelling Out Evidence: NIST Ballistic Standard Helps Tie Guns to Criminals

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Image of shell casing

Thanks to a new reference standard developed by Commerce's National Institute of Standards and Technology (NIST), law enforcement agencies will have an easier time linking the nearly 200,000 cartridge cases recovered annually at U.S. crime scenes to specific firearms.

Cartridge cases—the empty shells left behind after a gun is fired—are routinely sent to forensic laboratories for analysis when they're found at a shooting scene. Using a specialized microscope called an Integrated Ballistic Identification System (IBIS), lab technicians acquire digital images of three markings, or "signatures," impressed on the cartridge case by the gun that fired it. These signatures—the firing pin impression, the breech face impression and the ejector mark—are unique when fired from a specific firearm and can serve as "fingerprints" for that gun once the digital images are entered into a national database known as the National Integrated Ballistic Information Network (NIBIN).

For forensic examiners to reliably match recovered cartridge cases with ones whose signatures have been recorded in the NIBIN, they need to have confidence in the accuracy of the equipment and procedures used to make the link. That's where NIST's new "standard casing" comes in. The standard contains two items: an exact replica of a master cartridge case with distinct signature marks (obtained from the Department of Justice's Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF), and a "golden" digital image of those same signatures that reside on the NIBIN.  Full Tech Beat story

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Signatures don't become fingerprints by entering into a database

I remain confused by your story. You state that the signatures become "fingerprints" once they are entered into a database. Is that true and correct?

Fingerprints and signature are metaphors

We used the terms "fingerprints" and "signature" as metaphors to help explain the very technical aspects of ballistics science. We are simply trying to say that each shell has unique markings and once those markings are entered into a database, they can be searched and used to compare with other shells to see if the same weapon fired them.