Accuracy and Reproducibility of Bullet Comparison Decisions by Forensic Examiners

Published

November 4, 2024

Author(s)

R. Austin Hicklin, Connie Parks, Kensley Dunagan, Brandi Emerick, Nicole Richetelli, William Chapman, Melissa Taylor, Robert Thompson

Abstract

Few studies have been conducted assessing the accuracy and reproducibility of bullet comparison decisions by firearms examiners, and no previous studies have evaluated accuracy of examiners' decisions when comparing 1) damaged bullets, 2) comparisons of questioned bullets, or 3) the effects on decision rates of using jacketed hollow-point (JHP) vs. full metal jacket (FMJ) bullets. This paper presents the results of a study in which 49 practicing forensic firearms examiners conducted 3,156 comparisons of bullets. The comparisons included bullets ranging in quality, bullets from different types of ammunition, and bullets fired from various makes and models of firearms. The study included evaluation of two scenarios commonly used in operational casework: questioned-questioned (QQ) comparisons of two unknown bullets, and known-questioned (KQ) comparisons in which an unknown bullet is compared to three known exemplars from a single firearm. Key findings: after controlling for other factors, QQ vs. KQ comparisons have relatively limited effects on decision rates; rates of inconclusive responses were inversely related to the quality of the questioned bullets; bullets fired from pistols with polygonal rifling resulted in more inconclusive or unsuitable responses than conventional rifling; on nonmated comparison sets, the rate of (true) exclusions was particularly high when comparing different caliber bullets, and was higher on comparisons of different makes/models of firearms vs. the same model of firearm; comparisons in which different types of ammunition were fired from the same firearm had a high rate of erroneous exclusions; decision rates differed notably among the models of firearms; and decision rates varied notably among the participants. Because the measured rates vary dramatically due to these various factors, we recommend against using overall decision rates to summarize the results of this study.

Citation

Forensic Science International

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.forsciint.2024.112287

Local Download

Keywords

forensics, firearms, decision analysis, bullets, error rates

Citation

Hicklin, R. , Parks, C. , Dunagan, K. , Emerick, B. , Richetelli, N. , Chapman, W. , Taylor, M. and Thompson, R. (2024), Accuracy and Reproducibility of Bullet Comparison Decisions by Forensic Examiners, Forensic Science International, [online], https://doi.org/10.1016/j.forsciint.2024.112287, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958032 (Accessed September 29, 2025)