Firing pin impressions: a valuable feature for determining the orientation of the weapon at the time of shooting. (November 2020)

• Record Type: Journal Article
• Authors: Manzalini, Valentina; Frisia, Michele; Scomazzoni, Marco Leonardi; Del Ángel, Vanessa Fossati; Causin, Valerio
• Is Part Of: Forensic science international. Volume 316(2020)
• Publication Date: 2020-11
• Subjects: Ballistics -- Firearm identification -- 3D profilometry -- Microscopy -- Orientation of the weapon; Medical jurisprudence -- Periodicals; Chemistry, Forensic -- Periodicals; Forensic Medicine -- Periodicals; Médecine légale -- Périodiques; Chimie légale -- Périodiques; Gerechtelijke geneeskunde; Gerechtelijke chemie; Gerechtelijke psychiatrie; Chemistry, Forensic; Medical jurisprudence; Electronic journals; Periodicals; Electronic journals; 614.1
• DOI: 10.1016/j.forsciint.2020.110519
• Languages: English
• ISSNs: 0379-0738

Abstract

Highlights: 3D topography is applied to the characterisation of firing pin impressions. Orientation of the weapon influences the efficiency of combustion and bullet speed. The marking of the cartridge case depends on the orientation of the weapon. Firing pin indentation reflects the orientation of the gun at the time of firing. The reconstruction of shooting incidents can be achieved. Abstract: Sometimes the firearm forensic examiner is required to provide information useful to discriminate between suicide, homicide or accident, or between contradictory reconstructions of the events (like attempted murder versus accidental discharge). In such situations, knowledge of the position and orientation of the firearm at the time of firing can be of fundamental help for the reconstruction of events. To achieve these goals, the analysis of the firing impressions is very important. In this study, the cartridge cases shot with three different revolvers aiming at three different spatial orientations (vertical upwards, horizontal or vertical downwards) were studied. The depth and morphology of the firing pin impression was characterised by optical microscopy and quantified by a surface topography analysis. The orientation of the firearm significantly modified the morphology and depth of the firing pin impression: ammunition fired upwards had the deepest firing pin impression, those fired downwards had the shallowest. Such behaviour was attributed to the different geometry of the firing pin-primer cup interaction and to the different pressure exerted by the primer as the orientation of the weapon changes. Therefore, this work has shown that a suitable protocol of morphological and topographical analysis can be set up to understand if a shot by a revolver was fired holding the weapon upwards, downwards or horizontally.