Author ORCID Identifier

https://orcid.org/0009-0005-4877-718X

Semester

Summer

Date of Graduation

2025

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Keith Morris

Committee Member

Jeremy Dawson

Committee Member

Michael Neel

Committee Member

Casper Venter

Abstract

Due to criticisms towards the firearm and tool mark examiner community by several reports and other scientists, especially in regards to subclass characteristics, there was an apparent need for a study to provide deeper insight into (1) the manufacturing processes and the produced marks; (2) transfer of those marks to cartridge cases, if applicable; (3) into examiner assessment of the identification of subclass and individual characteristics. These needs were addressed, in part, by the objectives of this research study: characterize different manufacturing methods and the breech faces thus produced to evaluate the presence of subclass characteristics, reproducibility of subclass characteristics on spent cartridge cases of various ammunition brands, and to evaluate the consistency of firearm examiners in distinguishing subclass characteristics from individual characteristics.

Four manufacturing processes were used to consecutively manufacture breech face inserts for a Thompson/Center® (T/C®) Contender® G2 pistol as the firearm of choice because of its capability of interchangeable breech face inserts which allows the manufacturing of consecutive breech face inserts to simulate different firearms. One hundred and ten breech faces were manufactured in two phases (Group A and B). A Sensofar® S neox 3D optical profiler was used to collect the 3D topographical scans of the breech faces and their resultant test fires which provided a total of 220 breech face scans and 3,000 cartridge case scans (includes before and after finishing method). The congruent matching cells algorithm (CMC) developed by the National Institute of Standards and Technology (NIST) was used to pairwise compare all breech faces and test fires within their respective group by manufacturing processes. These results were used to assess the presence of subclass characteristics from the manufacturing processes. It was found that the broached and plunge milled manufacturing methods produced some subclass characteristics on the breech faces, whereas the turned and face milled manufacturing methods did not. The marks from the manufacturing methods transferred some of the subclass characteristics to their respective cartridge cases. Once finishing methods were applied, some, if not all, of the subclass characteristics were removed and therefore reduced the amount transferred to the cartridge cases. The glass bead blasting finishing method was a more abrasive finishing method compared to the tumbling method.

Five primer brands were compared to assess the effect they had on the transfer and presence of subclass characteristics from the broached breech faces, both unfinished and finished. A total of 5,000 cartridge cases were collected and inter- and intra-brand comparisons were performed using the CMC algorithm. Performance was determined by receiver operating characteristic (ROC) curves and area under the curve (AUC) analysis. The Federal Match primers marked and performed the best when compared to the other primer brands. The order of performance by primer brand was Federal Match, Winchester, CCI, Sellier & Bellot, and Remington. Several error rates and the equal error rates were also calculated to assess the performance of each primer brand.

Lastly, firearm examiners were evaluated by labeled images of cartridge cases that contained different characteristic types (i.e. class, subclass, and individual). Eight firearm examiners participated and were qualitatively assessed for both reproducibility and repeatability. Generated heatmaps of each mark type within each group were performed. It was found there was consensus within each group for most images. The areas which were marked subclass and individual characteristics were overlaid and it was noted that the experimental group had more areas that were labeled as both characteristic types compared to the control group. The repeatability images demonstrated that each participant performed relatively well replicating their mark up on the repeated images. More formal and practical training in identification of subclass characteristics by firearm examiners is suggested from the results of this study.

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