Visualization of the powder pocket and its influence on staining in firearm barrels in experimental contact shots

Postmortem Computed Tomography and Magnetic Resonance Imaging of an Abdominal Gunshot Wound

The use of postmortem computed tomography (CT) has been described in many articles concerning gunshot injuries. Postmortem magnetic resonance imaging (MRI) for better assessment of soft tissue injuries has also been mentioned in the literature, albeit much less often. The use of postmortem MRI for abdominal gunshot wounds has not been previously presented in the literature. The present case report describes the findings of an abdominal gunshot wound detected by postmortem CT and MRI, followed by an autopsy. The main imaging findings on CT were a hyperdense ring at the entrance wound, which indicated the muzzle imprint mark, a hyperdense region beneath the skin, which was suggestive of combustion residue, gas cavities surrounding the bullet path, which might be related to the temporary cavity, and a fracture of the 13th rib on the left. Magnetic resonance imaging provided a clear depiction of defects in the muscle tissue and peritoneal fat, as well as an injury to the left kidney and a large volume of blood in the abdominal cavity. Computed tomography combined with MRI provided a descriptive presentation of the intracorporeal trajectory noninvasively. Autopsy confirmed the radiologic findings but additionally revealed further relevant findings, which were not detected radiologically, such as a duodenal perforation. Autopsy also detected subendocardial hemorrhages and shock kidney, which were consistent with severe blood loss.The imaging findings and their interpretations are discussed in this case report, as well as the role of CT and MRI in the assessment of abdominal gunshot wounds compared with autopsy.

Study of backspatter using high-speed video of experimental gunshots

Backspatter is biological material that is ejected from the entry wound against the line of fire. This phenomenon was also observed in wound ballistic simulations using so called "reference cubes" (12 cm edge length, 10% gelatin, 4 °C, paint pad beneath the cover). High-speed video records from 102 experimental shots to these target models using full metal jacketed bullets in the calibers .32 auto, .38 special, 9 mm Luger and .357 Magnum were analyzed for chronology, morphological appearance and velocity of fluid ejection. Generally, a short tail splashing of surface material occurred when the bullet was penetrating the target. In 51 shots from distance (≥ 5 cm), regardless of caliber and shot range, a linear jet of fluid started in connection with the first collapse of the temporary cavity. The initial velocity of the jet was measured between 6 and 45 m/s. The jet was streaming on for about 60 to 100 ms with a stochastic deviation of ± 13° to the horizontal. Close range and contact shots showed earlier and faster (up to 330 m/s) backspatter depending on the cartridge and the gap between muzzle and target. Gaseous aerosol-like spray and cone-like spatter indicated an increasing influence of muzzle gases with decreasing shot range. Even under standardized experimental conditions, variations of backspatter were observed in near/contact shots.

The influence of muzzle gas on the temporary cavity

Shot range, the muzzle-target distance, is a crucial parameter for forensic reconstruction of deaths by firearms. In a large number of cases, especially suicides, the forensic pathologist is confronted with contact or near-contact shots, where muzzle gases play an additional role. This study was conducted to systematically investigate the influence of muzzle gases on the temporary cavity (TC). A total of 72 shots were fired using full metal-jacketed bullets in four forensically relevant calibres from 10-, 5-, 3-, 2- and 1-cm distance and in close contact. Target model was the so-called reference cube (10% gelatine at 4 °C) with 12-cm edge length. The TC was recorded using high-speed video (HSV). Cross-sectional analysis was performed by cutting the blocks to 1-cm slices, which were evaluated by applying the polygon method. The TC of shots from 10 and 5 cm distance had a tubular form. This aspect changed depending on the cartridge with decreasing distance (≤ 3 cm) into a pear-like form, which was typical for contact shots. The cumulated heights of the TC increased with decreasing distance below 3 cm. Contact shots approximately doubled the extension of the TC compared with exclusive energy transfer. Whereas HSV documented an increasingly asymmetric profile with ballooning at the entry side, cross-sectional analysis of cracks in gelatine resulted in convex graphs with only slight asymmetry for contact shots. Additional damage in gelatine was detected for 3-cm distance or less in calibre .357 Magnum and ≤ 2 cm for .32 auto, .38 special and 9mm Luger. The increasing influence of muzzle gas pressure is detectable with decreasing shot range below 3 cm.

Interpol review of forensic firearm examination 2016-2019

This review paper covers the relevant literature on forensic firearm examination from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

The deceleration of bullets in gelatine - A study based on high-speed video analysis

The velocity of a projectile is of crucial importance to calculate its kinetic energy. The study was performed to investigate if a measurement of the velocity profile of a bullet in gelatine was feasible using high-speed video. More than 50 records captured with a SA-X2 Photron camera at 40,000 fps (40k) and 10 μs exposure time were analysed frame by frame. A measurement accuracy of one pixel could be realised. Records of free flying bullets with known velocity served as a control. In further experimental shots from distance the "12 cm reference cube" was used as target model. 18 full metal jacketed bullets and 20 deforming bullets in forensically relevant calibres were fired. In addition 11 expanding bullets were studied with a close-up setting of the camera and 81,000 fps (81k) at 2.5 μs exposure time. A quasi-constant deceleration of the FMJ bullets in gelatine with a relative loss of velocity of 8.4% (.32 auto) and 13.2% (9 mm Luger) was observed. Expanding bullets showed a much higher deceleration and a relative loss of about 56% for the copper hollow point bullet and 73% for the .32 auto Gold Dot. The targeted analysis of the .32 auto Gold Dot based on 81k videos revealed an abrupt drop of the bullet velocity within the first 75 μs, the time needed for full expansion. The deformation of the Action-4 (9 mm Luger) was completely achieved within the first 2 cm of gelatine. After the deformation of the bullet the final deceleration was approximately constant. This could be demonstrated successfully by separating the deformation process experimentally from the final deceleration of the deformed bullet.

Rearward movement of the slide in semi-automatic pistols: a factor potentially influencing the configuration of muzzle imprint marks in contact shots

A muzzle imprint mark is a highly diagnostic finding, which indicates a contact shot. In many cases, it also provides additional information on the type of the weapon used and on the way in which it was held at the time of firing. In semi-automatic pistols, some constructional elements constituting the muzzle plane move to the rear together with the slide, which may prevent them from causing a corresponding imprint close to the bullet entrance hole. The present study comprises 30 consecutive autopsy cases of fatal contact shots to the head inflicted with semi-automatic pistols. The imprint marks accompanying the entrance wounds were compared with the muzzle ends of the respective weapons both before and after retracting the slide. It turned out that in a considerable number of cases (3 out of 30), the retractable parts were not depicted or only to a minor degree as components of the imprint mark. In order to validate the presumed correlation, experimental shots were fired to composite models using pistols in which the movable and the stationary parts forming the muzzle plane were dyed with different paints. Thus, it could be demonstrated that the muzzle imprint preferentially mirrors the front sides of the stationary parts such as the barrel end, the recoil guide, and the gun housing. Immediately after discharge, the slide and the ballooning skin of the bullet entrance site move in the same direction. The stationary parts of the weapon block the expansion of the skin bulging towards the muzzle, so that the skin gets firmly pressed against them. The dynamic interaction between the gun and the entrance region resulting in a characteristic imprint mark could be visualized by the use of a high-speed motion camera recording test shots to different composite models.

Distortion of the temporary cavity and its influence on staining in firearm barrels

After contact shots to the head, biological traces can be found inside the barrel of the firearm. Experimental protocols to generate this sort of staining, using 12 cm gelatin cubes containing thin foil bags filled with acrylic paint, human blood, and radiocontrast agent, have been developed. Previous research on shots fired at a distance has shown the underlay sustaining these gelatin cubes has an influence on experimental results. This study was conducted to investigate the role of the sustaining base of the gelatin blocks during contact shots, and its influence on the staining result inside firearm barrels. Eighteen contact shots were performed using 22 LR, 32 ACP (7.65 Browning) and 9 mm Luger semi-automatic pistols. With each pistol, shots were fired onto six gelatin cubes; three placed upon a rigid platform and three upon an elastic underlay. The shots were recorded by a high-speed video camera as they penetrated the gelatin cube. Any staining present inside the firearm barrels after the shots were fired was documented by endoscopy. Cross sections of the gelatin blocks were then compared to the high-speed video. It was found that the nature of the staining inside the barrel was not influenced by the underlay sustaining the target model. In the experiment using a 9 mm Luger, the rigid counterfort provoked a visible distortion of the temporary cavity, but, cross sectional analysis of the gelatin cubes did not reveal a relevant influence of the sustaining underlay on the crack length in the gelatin. This could be explained by a secondary expansion of the temporary cavity left by the projectile as a consequence of subsequent inflow of muzzle gases.

The influence of the counterfort while ballistic testing using gelatine blocks

In wound ballistic research, gelatine blocks of various dimensions are used depending on the simulated anatomical region. When relatively small blocks are used as substitute for a head, problems with regard to the expansion of the gelatine block could arise. The study was conducted to analyse the influence of the material the gelatine block is placed upon. Thirty-six shots were performed on 12 cm gelatine cubes doped with thin foil bags containing acrylic paint. Eighteen blocks each were placed on a rigid table or on a synthetic sponge of 5 cm height. Deforming bullets with different kinetic energies were fired from distance and recorded by a high-speed video camera. Subsequently, the gelatine cubes were cut into 1 cm thick slices which were scanned using a flatbed scanner. Cracks in the gelatine were analysed by measuring the longest crack, Fackler's wound profile and the polygon (perimeter and area) outlining the ends of the cracks. The energy dissipated ranged from 153 to 707 J. For moderate energy transfer, no significant influence of the sustaining material was discerned. With increasing dissipated energy, the sponge was compressed correspondingly, and the cracks were longer than in gelatine blocks which had been placed on a table. High-speed video revealed a loss of symmetry and a flattened inferior margin of the temporary cavity with energies superior to approx. Two hundred Joules when the blocks were placed on a rigid platform. However, 12 cm gelatine cubes showed material limits by a non-linear response when more than 400 J were dissipated for both rigid and elastic sustainment. In conclusion, the smaller the gelatine blocks and the greater the energy transfers, the more important it is to take into account the counterfort of the sustaining material.

The reference cube: A new ballistic model to generate staining in firearm barrels

After contact shots to the head biological traces can be found inside firearm barrels. So far silicone coated, gelatin filled box models were used to generate such staining according to the triple contrast method (mixture of acrylic paint, barium sulfate and blood sealed in a thin foil bag). This study was conducted to develop a transparent ballistic model allowing contact shots. Gelatin filled polyethylene bottles with and without a silicone coat were tested in comparison to non-covered gelatin blocks. Finally, thin foil bags of 5 cm × 5 cm dimension were glued on a synthetic absorbent kitchen wipe on top of which 1 L 10% gelatin solution was molded to create blocks of 8.5 cm length. A kitchen wipe with a paint pad on its inside formed the front of the cube. Three contact shots each with a 9 mm Luger pistol and a .38 special revolver were performed on all model variations. The staining was documented by endoscopy and swabs gathered from both ends of the barrel were analyzed by quantitative PCR. Reliable staining was achieved using the front covered gelatin block with comparable results to the silicone coated box model used before. For further research using ballistic models to simulate a human head a symmetric form of the gelatin block such as a cube is recommended.