Statistical Approaches to Type Determination of the Ejector Marks on Cartridge Cases

While type determination on bullets has been performed for over a century, type determination on cartridge cases is often overlooked. Presented here is an example of type determination of ejector marks on cartridge cases from Glock and Smith & Wesson Sigma series pistols using Naïve Bayes and Ra...

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Bibliographic Details
Published in:Journal of forensic sciences 2018-03, Vol.63 (2), p.431-439
Main Authors: Warren, Eric M., Sheets, H. David
Format: Article
Language:English
Subjects:
Bayesian analysis
Crime laboratories
ejector marks
Firearms
Forensic ballistics
forensic science
Glock
morphometrics
Multivariate analysis
Naïve Bayes classification
Projectiles
Small arms
Smith & Wesson Sigma
Test firing
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Summary:While type determination on bullets has been performed for over a century, type determination on cartridge cases is often overlooked. Presented here is an example of type determination of ejector marks on cartridge cases from Glock and Smith & Wesson Sigma series pistols using Naïve Bayes and Random Forest classification methods. The shapes of ejector marks were captured from images of test‐fired cartridge cases and subjected to multivariate analysis. Naïve Bayes and Random Forest methods were used to assign the ejector shapes to the correct class of firearm with success rates as high as 98%. This method is easily implemented with equipment already available in crime laboratories and can serve as an investigative lead in the form of a list of firearms that could have fired the evidence. Paired with the FBI's General Rifling Characteristics (GRC) database, this could be an invaluable resource for firearm evidence at crime scenes.
ISSN:0022-1198
1556-4029
DOI:10.1111/1556-4029.13529