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BookmarkScienceDaily (May 15, 2002) — Two robberies take place at different sites in New York City a few days apart.Police suspect that the same person is responsible but only have small pieces of evidence with which to make the link: bullets and casings found at the two locations. Thanks to new “standard bullets and casings” from the National Institute of Standards and Technology (NIST), any forensic scientist trying to match these bullets and casings could be confident with his or her results.
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Ballistic evidence is considered valuable because each gun’s firing pin and ejection mechanism imparts distinctive markings — known as “signatures” — on fired bullets and ejected casings. The computerized optical-imaging instruments used to examine these signatures must be calibrated for accuracy.
To provide the tools needed to do the critical calibrations, NIST has manufactured standard bullets — known as NIST Reference Material (RM) 8240 — and standard casings — known as NIST RM 8250 — with identical signatures. The signatures on each bullet and casing RM created by NIST are exactly the same as those on every other corresponding artifact in the two series. Quality bullets previously used in forensic laboratories were produced by a standardized shooting procedure and, therefore, exhibited minute changes in signatures over time due to gun wear and environmental conditions.
NIST researchers also are working on a “virtual” or digital bullet signature standard that crime laboratory personnel can access with their computer from the national laboratory center at the Bureau of Alcohol, Tobacco and Firearms (ATF) and the Federal Bureau of Investigation (FBI).
