Consecutive and Random Manufactured Semi-Automatic Pistol Breech Face and Fired Cartridge Case Evaluations
Ashley Chu, Shannon McClorry, Roy Geiss, David Read, David Howitt, Michael Hill
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ABSTRACT
This report describes our work on the evaluation of the impression markings on cartridge cases fired from semi-automatic pistols to determine to what extent these markings can be used to individualize a firearm and whether they can be quantified in terms the possibility that it occurred by random chance. We have been able to demonstrate that the size of the individual regions of corresponding topography on the breech faces of cartridge cases fired from the same slides were consistently larger than those that were consecutively manufactured and that there are other aspects to the matching that are not reflected by cross correlation analysis. The conclusions that can be drawn from this work are that the differences between the cross-correlation coefficients from matching and non-matching cartridge cases can not only be increased by focusing on particular sized regions of correspondence but that other approaches such as pattern recognition can also be effectively used to supplement the cross correlation techniques. Thus by modifying the algorithms that determine the similarities it should be possible to increase the number of cartridge cases that can be added to a database before it will be overwhelmed by false positives.