Bullet Caliber and Type Categorization from Gunshot Wounds in Sus Scrofa (Linnaeus) Long Bone
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J Forensic Sci,2019 doi: 10.1111/1556-4029.14004 TECHNICAL NOTE Available online at: onlinelibrary.wiley.com ANTHROPOLOGY Bailey J. Henwood,1 B.Sc. (Hons); Tracy S. Oost,1 B.Sc. (Hons); and Scott I. Fairgrieve ,1 Ph.D. Bullet Caliber and Type Categorization from Gunshot Wounds in Sus Scrofa (Linnaeus) Long Bone ABSTRACT: Studies on ballistic trauma to the ribs and thorax, cranium, and long bones demonstrate the potential of obtaining a bullet cal- iber from an entrance wound. In order to validate prior research on caliber estimation in bone tissue and assess the viability of bullet type deter- mination based on the macroscopic evidence at the entrance wound, thirty fleshed pork (Sus scrofa) shoulders (humeri) were shot with either lead or copper jacketed bullets in one of three calibers; 0.22, 9 mm, or 0.38. Overall, our findings are consistent with previous research indicat- ing that calibers can be grouped into “small” and “large” categories. Bullet type, lead or copper jacket, can be ascertained based on cortical flaking and the analysis of materials deposited around the entry wound. The addition of this evidence holds value in cases where no firearm or ballistic evidence is recovered from a crime scene. KEYWORDS: forensic science, forensic anthropology, ballistics, gunshot wound, bullet caliber, bullet type Evidence of ballistic trauma to the ribs and thorax (1,2), cra- is the potential deposit of lead or copper to the bone from the nium (3–5), and long bones (6,7) can yield important investiga- bullet upon impact. Entry wounds were examined to determine tive information. Research using the flat bones of the cranium if any differences between wounds from lead versus copper jack- found that the minimum diameter of the entrance wound can eted bullets exist. Scanning electron microscopy–electron disper- lead to a general caliber size estimation (3–5). “Small” calibers, sion X-ray (SEM-EDX) was also utilized to analyze any such as 0.22, 0.25, 0.28, and 0.32, have been successfully distin- potential trace bullet wipe left upon impact. guished from “large” caliber bullets, such as 0.38 or 9 mm (3– Some common issues observed in previous studies include the 5). Berryman et al. (3) noted that the entrance wounds are within sheer number of calibers, and examining the effect intermediate two measured calibers of the actual caliber used. While these targets may have on the flight path of a bullet as well as the broad categories do not allow for specific caliber estimation, range of bullet designs and how bone reacts to the different investigators can eliminate various calibers of the suspected forces involved (2–7). The elastic modulus of a bone may be bullet. exceeded at different loads depending on the bone’s architecture, High-velocity trauma inflicted on bone produces instantaneous hence affecting the overall fracture pattern. Bone density, failure of the bone without deforming the fragments. This per- anatomical region, and age of the bone must also be considered mits reassembly for entry wound analysis (4,5,7). This study uti- as important variables in wound dynamics (4,5,7,9). lizes these observations to attempt to determine caliber as well The microstructure of bone plays a critical role in mitigating as note any changes to the bone based on the type of bullet the formation of cracks due to impacts (10). The energy from an used. impact is diverted along the lamellar cement lines as well as The specific categorization of bullet type, be it lead or copper, through the fluids contained in the Haversian and Volkman’s has the potential to add another dimension to the evidence of canals, canaliculi, and lacunae. The totality of the microstruc- ammunition used. DiMaio defines a bullet wipe as the ring of ture’s individual energy absorption results in slowing the rate of soot around the entry point of a bullet in clothing, contrary to crack formation and may arrest propagation altogether. A high- the belief of it being lead from the bullet passing through the energy event such as a ballistic impact results in fast propagating fabric (8). He states that only the first layer of clothing will have cracks that overcome the mitigating effect of the lamellae (10). this “bullet wipe” or soot ring. As this study did not analyze any Other studies detail crack propagation on a macroscopic and his- clothing or soft tissue, a bullet wipe in the context of this study tological level (11–13). The diaphysis of a long bone is essentially a dense cortical bone cylinder with a medullary cavity. The dense cortical bone 1 Forensic Osteology Laboratory, Department of Forensic Science, is required to provide stability and rigidity to the skeleton (14). Laurentian University, Sudbury, Ontario, P3E 2C6 Canada. Corresponding author: Scott I. Fairgrieve, Ph.D. E-mail: sfairgrieve@lau- The porous trabecular portion is made up of bony spicules rentian.ca arranged in trajectories along the major tensile and compressive Received 31 Aug. 2018; and in revised form 14 Nov. 2018; accepted 30 lines. The role of trabecular bone is to dampen stresses applied Dec. 2018. to the articular surface (15). © 2019 American Academy of Forensic Sciences 1 2 JOURNAL OF FORENSIC SCIENCES When hit by a high-velocity impact as seen in ballistic bullets and can absorb some of the energy of the impact and wounds, the load is applied so rapidly that the bone reacts as a flatten. A full copper jacket resists yielding to the forces stiff and brittle material (16). The energy is projected through imparted onto the bone and the bullet largely retains its original the outer table of cortical bone and explodes into the medullary shape (8). cavity. Due to this mechanism of energy propagation, a beveled entrance wound is found in long bones that have undergone bal- listic trauma (2,17). This results in many small fragments that Materials and Methods exhibit no deformation and can be reconstructed almost seam- Sample Description lessly (5,7,16). Directionality of a gunshot wound to a bone can be determined utilizing both the bone displacement seen in the Thirty specimens of Sus scrofa L. (domestic pig) humeri fragments as well as external beveling noted on the entry sur- were used as an analog for human long bone. Each pork shoul- face, which reinforces the importance of reassembling the wound der was intact, with skin and underlying muscle tissues attached area (1,2). to the bone. Each of these specimens was shot once with a The different components of terminal, or wound, ballistics handgun at close range (approximately 0.75 m) perpendicular to when assessing bone damage are essential. Terminal ballistics the length of the diaphysis using a specific caliber. After shoot- has been greatly explored concerning soft tissue and is well ing, each specimen was stored in a freezer until the removal of understood. The velocity at which a bullet enters the body can soft tissue. The resulting bone fragments for each specimen have a large effect on the type and size of wound created. The were stored at room temperature (~19°C) in a storage cabinet faster a bullet is moving through tissue, the less time the tissue in the laboratory. Reconstructed humeri were stored in the same has to react to the impact. The velocity is directly related to the manner. cavitation left in the wound tract. Temporary cavitation is the elastic reaction of the tissue to the projectile as surrounding soft Firearms and Ammunition tissue is forced outward by the bullet and almost immediately fills the space behind the bullet as it passes (18). Permanent cav- Three different calibers of bullets were used: 0.22, 9 mm, and â itation is caused by the shearing and compressive forces of the 0.38. The 0.22 caliber firearm used lead round-nose Blazer projectile as it tracks and tears through the tissue in a way that it CCI 0.22 long rifle ammunition. The 9 mm ammunition was a â cannot fall back into the wound path (18). The faster the bullet full copper jacket Dominion brand centerfire bullet. Finally, â moves through the soft tissue, the larger the permanent cavity. lead round-nose Dominion brand centerfire 0.38 special ammu- In flight, bullets tend to yaw. Yaw is the manner in which a bul- nition was used. The firearms used were a High StandardTM let tumbles sideways during its flight. When a bullet has higher Supermatic, a Forjas TaurusTM Semi-Automatic, and a Smith and â velocity, it is able to physically spin faster and the yaw is Wesson Model 639, respectively. It is important to note that reduced (19). With less yaw, a bullet is more stable and there- 9 mm and 0.38 calibers are in fact the same size. A 0.22 caliber fore enters the tissue at a straighter trajectory. If a bullet has bullet measures 5.65 mm in diameter, while a 9 mm and a 0.38 more yaw, the trajectory has a greater angle of entry into the soft caliber each measure 9.00 mm. tissue and, consequently, the cavity is larger (19). The bullet caliber influences the velocity due to the differ- Shooting ences in grain (mass). To illustrate this, the 9 mm ammunition used in this study is 124 grain, while the 0.38 ammunition is The pork shoulder segments were placed on their side, parallel 158 grain. While the two calibers measure the same physical to the ground. There were ten specimens used for each caliber, dimension of 9 mm, the 0.38 bullet is heavier and will have a and each shoulder was shot once with the intended target being lower speed but have a higher momentum upon impact.