Introduction: Special deformation bullets were developed for police forces to achieve a defined penetration depth (avoiding over-penetration) and a controlled energy transfer (avoiding collateral damage). This article focuses on Action 4, SECA and QD-PEP bullets. These 9 mm bullets were specially designed for controlled deformation. The characteristic slight mushrooming with a front cross-section of approximately 11.5 mm after entering a ballistic simulant was verified in ballistic tests. To achieve such slight mushrooming, the projectile's core is hollowed. The purpose of this study was to investigate the feasibility of visualising the hollowed cores of Action 4, SECA and QD-PEP bullets using a standard clinical computed tomography (CT) scanner for non-invasive identification of these special bullets from police ammunitions.
Methods: First, undeformed specimens were scanned to reveal the shape of the hollowed core of each type of special bullet. Second, Action 4, SECA and QD-PEP bullets were fired towards animal cadaver models to visualise their hollow core after deformation inside biological tissue. Third, two reviewers were tasked with identifying special bullets from police ammunition (Action 4 bullets: n = 3) among 10 CT examinations of humans with lodged projectiles who were selected by the supervisor of the study.
Results: The CT scans of the undeformed specimens revealed the special design of the bullets' metal core. All special bullets from police ammunitions that were fired towards an animal cadaver model demonstrated the characteristic slight mushrooming. In accordance with the CT scans of the undeformed bullets, visualisation of the individual internal cavities of the special bullets allowed the Action 4, SECA and QD-PEP bullets to be clearly distinguished. With regard to the real forensic cases, both reviewers clearly identified each of the three Action 4 bullets among all other lodged projectiles.
Conclusions: This study demonstrates the feasibility of identifying Action 4, SECA and QD-PEP bullets from special police ammunitions by CT. The individual shapes of the cavity inside the bullets were clearly visible on CT. In situ identification of these bullets can aid in the assessment of injuries, and since these bullets are fabricated from non-ferromagnetic metals, their clear identification allows for magnetic resonance imaging (MRI) without the risk of bullet movement inside the body due to the magnetic pull of the MRI unit. Furthermore, this approach could be of great interest to forensic investigators if patients who received gunshot wounds underwent non-operative treatments and the projectile remains in the body. Since the use of CT is also increasing for medico-legal post-mortem examinations, the identification of lodged projectiles is of interest for a virtual autopsy or 'Virtopsy'.
Keywords: Action 4 bullet; Law enforcement ammunition; QD-PEP bullet; forensic radiology; police ammunition; radiologic wound ballistics.