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Identifying Persistent and Characteristic Features in Firearm Tool Marks on Cartridge Cases



Johannes A. Soons, Robert M. Thompson, Jun-Feng Song


To address concerns of subjectivity in firearm evidence examination, algorithms are being developed to compare firearm tool marks imparted on ammunition and generate a quantitative measure of similarity. The goal of this paper is to demonstrate a new algorithm that is able to identify the regions in the breech face impression of a cartridge case that are consistent between firings and that also contribute strongly to the normalized cross correlation similarity metric. The result is a representation of the impression that emphasizes features that are both significant and persistent across firings. This characteristic surface is useful for understanding the variability and persistence of the tool marks created by a particular firearm and can provide improved discrimination between the comparison scores of samples fired from the same firearm and the comparison scores of samples fired from different firearms. The algorithm also provides a convenient method for visualizing areas of similarity that may be useful in examinations by trained examiners and provides quantitative support for visual comparisons.
Surface Topography: Metrology and Properties


Forensics, Firearm and Tool Mark Examination, Similarity Maps, Feature Correlation


Soons, J. , Thompson, R. and Song, J. (2017), Identifying Persistent and Characteristic Features in Firearm Tool Marks on Cartridge Cases, Surface Topography: Metrology and Properties, [online],, (Accessed June 14, 2024)


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Created December 12, 2017, Updated June 23, 2020