Measurements completed for 20 RM 8240 standard bullets.

Scratches on a bullet recovered at a crime scene can be as incriminating as fingerprints. Unfortunately, methods for analyzing these tell-tale forensic "signatures" still entail manual comparisons, making firearms-ballistics databases impractical. NIST scientists, with input from industrial and government partners, developed "standard" bullets--bullet-shaped artifacts with a series of surface profiles that can be used for testing the forensic equipment and operators. These standard bullets, officially called Reference Material (RM) 8240, are still under-going final testing.

Surface profile measurements of 20 RM 8240 standard bullets were completed in April 2003. These measurements were performed with a newly developed NIST bullet signature measurement system. A NIST proposed parameter and algorithm are used for quantifying the bullet signature differences between the RM bullets and a virtual standard for the bullet signatures. The virtual standard is a set of six digitized surface profile signatures, originally obtained from six master bullets shot at the Bureau of Alcohol, Tobacco and Firearms and the Federal Bureau of Investigation, using six different guns. By using the virtual signature standard as tool path information in a numerically controlled diamond turning machine at the NIST instrument shop, the 20 RM bullets were produced. The NIST proposed algorithm uses auto-and cross-correlation functions (ACF and CCF) for quantifying bullet signature differences. When the two compared signatures are exactly the same (point by point), their CCF would be equal to 100%. Measurement results showed that the CCFs for all 120 profiles (6 profiles on each of 20 bullets) are higher than 95%, and most of them are higher than 99%. These results demonstrate the high reproducibility of both the manufacturing process and the measurement system for NIST RM bullets.

A NIST associate from Drexel University and NIST scientists developed the measurement program. The measurement data will undergo further statistical analysis at NIST. A NIST workshop is scheduled for early June, preceding availability of the RM bullets to forensic agencies nationwide.

CONTACT: John Song, [phone]; [e-mail].