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Sarah B has been moved to a new group. Your group now has three members: Levi, Jon and G. As with fingerprints, every firearm has unique characteristics and, when fired, imprints unique signatures on the bullets and casings. By analyzing these ballistics signatures, examiners are able to connect a particular firearm to criminal acts. The NIST standard bullets and casings are being developed as reference standards for crime laboratories to help verify that the computerized optical-imaging equipment in those laboratories is operating properly. They will be used for instrument calibrations and measurement quality control, and have a potential use for enabling nationwide and worldwide ballistics measurement traceability and unification. The second set of prototype standard bullets are being designed with the size, shape, color and material as close as possible to real bullets. The bullet signature patterns of the standard bullets come from real bullets. These bullet signatures must be highly repeatable in different axial sections on the same standard bullet, and highly reproducible in a group of standard bullets. The numerically controlled (NC) diamond turning process was used at NIST for production of the first set of prototype standard bullets. Specially designed fixtures were used to hold the standard bullets on the diamond turning machine for manufacturing of the bullet signatures. The original bullet signatures were replicated from master bullets fired by a standardized shooting procedure at the National Laboratory Center of the Bureau of Alcohol, Tobacco and Firearms (ATF). The digitized bullet signatures were stored in a computer to control the NC diamond turning machine for the production of the standard bullets. Figure 1 shows a master bullet obtained by standardized shooting at the ATF's National Laboratory Center. Figure 1 also shows two prototype NIST standard bullets manufactured by NC diamond turning process. Figure 2 shows a comparison of the signatures of the master bullet (Figure 2a) and the standard bullet (Figure 2b). It can be seen that bullet signature on the standard bullet shows high fidelity with respect to the master bullet. Bullet signature comparisons were also made between different axial sections on the same bullet, and between different standard bullets. Comparison results showed high repeatability and reproducibility of bullet signatures of NIST standard bullets [ 1, 2 ].
 * **Standard Bullets and Casings** ||
 * || [[image:http://www.mel.nist.gov/div821/webdocs-13/bullets-1.jpg width="324" height="182"]] || || **Figure 1.** NIST standard bullets. ||
 * [[image:http://www.mel.nist.gov/div821/webdocs-13/bullets-2.jpg width="324" height="221"]] || || **Figure 2.** Bullet signature comparisons. || ||