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

The deceleration of full metal jacket bullets in compact target models - A new approach

The wounding potential of a projectile depends on its kinetic energy. The aim of the study was to investigate the deceleration of non-deforming full metal jacket handgun bullets (FMJ) in gelatine blocks of increasing length. The temporary cavity (TC) was visualized using a SA-X2 Photron camera. 126 test shots in 9 mm nominal calibre were fired under strict temperature control conditions (4°C) at small gelatine blocks ranging from 2 to 12 cm in length. The deposited energy was calculated based on the loss of bullet velocity through high-speed video analysis. The length of the TC was measured, when the TC reached its maximum height. The volume of the TC was approximated by a cylinder. Regression analysis showed a linear correlation between the length of the bullet path and the energy transfer. The constant deceleration of the FMJ bullets in gelatine up to 12 cm bullet path was confirmed across various brands and velocity ranges (270-450 m/s). Higher impact velocities correlated with increased loss of energy in the target medium. The shape of the bullet tip influenced the characteristic of deceleration. The volume of the tubular temporary cavity, derived from high-speed video records, was found to be proportional to the energy transferred. The proposed approach might be a valuable tool in advancing wound ballistics research.

The muzzle to target distance -staining inside different parts of the firearm barrel

Biological traces inside firearm barrels were observed as a result of contact shots to the head. The present study was conducted to investigate the influence of the muzzle to target distance on staining inside the anterior and posterior part of firearm barrels. Ninety-nine shots were fired to so-called reference cubes (10% gelatine, 12 cm edge length, embedded paint-blood-pad) using three current handguns. Shot range was varied from contact to 50 cm distance. High-speed cameras recorded external backspatter. Endoscopic examination assessed visible staining along the barrel. Each two swabbings were gathered from the anterior and the posterior part of the barrel. The first swabs were submitted to quantitative PCR, the second ones to DNA-RNA-co-extraction. Thorough mechanical and chemical cleaning was performed to avoid any contamination which was controlled by negative zero swabs after each cleaning. In single shots up to 50 cm distance, minimal, but DNA-positive sporadic traces were detected inside the barrel in vicinity of the muzzle. Visible complex staining varying in extent was observed in the anterior barrel part for 10 cm or less distance in dependence of the calibre. The posterior part showed detectable traces only after close range shots (< 5 cm). Generally staining inside the barrel decreased from the muzzle to the rear end, which correlated with the yield of DNA. Some contact shots did not cause any staining in the posterior part of the barrel despite massive external backspatter. Blood-specific miRNA was primarily found where DNA was detected. This experience encourages to take a second swab for RNA analysis. The amount of nucleic acids in the barrel at varying muzzle to target distances is subject to large variations between individual shots and therefore appears not suitable for a reliable determination of the shot distance in a particular case on its own. Instead, shot range estimation should also take into account morphology and distribution of traces inside the barrel.

The effects of certain intermediary target materials and their proximity to ballistic gelatin on jacketed hollow point bullet expansion

Expanding bullets are preferred by law enforcement because of their wounding potential and ability to avoid over-penetration which could result in unintended targets being struck by bullets that perforate their intended targets. Expansion failure for jacketed hollow point (JHP) bullets is commonly attributed to several causes including damage to the bullet's cavity, velocity loss, bullet destabilization and materials from intermediate targets filling the bullet's cavity which can cause expansion failure when the bullet subsequently impacts a soft, fluid-based target such as human tissue or ballistic gelatin. In this study, JHP bullets were fired into ballistic gelatin after passing through selected intermediate targets representing items common to shooting incidents. Velocity loss and bullet destabilization were not factors that contributed to the JHP bullets that experienced expansion failure; however, materials obstructing the bullets' cavities and damage to the bullets' cavities were considered causes for some of the JHP bullet expansion failures. It was determined through this research that most of the target materials caused JHP bullet expansion failure when shored against the ballistic gelatin, but when placed at distances of 7 ft. from the ballistic gelatin, bullets fired through the same target materials did expand. This original and unique study produced findings that are of significant value to shooting incident reconstruction experts and other forensic professionals as shooting incidents can call into question a victim's proximity to a wall or door when a bullet(s) perforated such a target material.

Lagrangian approach embed with discrete element method for extreme deformation study in frangible bullet designs fragmentation and penetration on viscoelastic ballistic gel

Development of a model for analyzing a bullet's impact is important in the military field to design a bullet with desired properties. This study uses a finite element model with a Lagrangian framework and Lagrange-discrete element method (DEM) model by ANSYS Explicit Dynamic to investigate the effect of frangible bullet designs on bullet deformation and penetration in ballistic gel setting. A modeling approach with ballistic gel can analyzed the extreme deformation of bullets much faster compared to the more resource intensive real life ballistic gel test. The study starts with developing a 3D model, then importing it to an ANSYS workbench to solve the problems. Overall, the results of Lagrange-DEM shows deeper penetration and better accuracy to represent the real life ballistic gel test than other simulation method. The fluted bullet design has a shorter penetration depth but a bigger temporary cavity diameter than the flat-nosed one due to its notch and asymmetrical design, which becomes the part that is easily deformed and leads to directional deformation.

Numerical study of the dynamic expansion behaviour of 9 mm expansion bullets in gelatine

Due to their limited penetration power, expansion bullets are known for their good effectiveness and less endangerment to bystanders, thereby playing an important role in the fight against terrorism and violence. This study considered 20 bullet configurations with different shape parameters influencing the motion and deformation of 9 mm expansion bullets in gelatine. Owing to the constraints of high-speed photography, experimental observations have limitations. However, through numerical simulation, this study found that the penetration process of the 9 mm expansion bullets through biological tissues, as represented by the gelatine block in this study, can be subdivided into four stages. Further, the expansion bullet is highly sensitive to the impact velocity, and did not completely expand when travelling at speeds below the critical velocity and over-expanded when travelling at speeds above the threshold velocity. The results of this study revealed the interaction mechanism between expansion bullets and gelatine, which are significant to ballistic wounding assessment and treatment of expansion bullets.

Ten years of molecular ballistics-a review and a field guide

Molecular ballistics combines molecular biological, forensic ballistic, and wound ballistic insights and approaches in the description, collection, objective investigation, and contextualization of the complex patterns of biological evidence that are generated by gunshots at biological targets. Setting out in 2010 with two seminal publications proving the principle that DNA from backspatter collected from inside surfaces of firearms can be retreived and successfully be analyzed, molecular ballistics covered a lot of ground until today. In this review, 10 years later, we begin with a comprehensive description and brief history of the field and lay out its intersections with other forensic disciplines like wound ballistics, forensic molecular biology, blood pattern analysis, and crime scene investigation. In an application guide section, we aim to raise consciousness to backspatter traces and the inside surfaces of firearms as sources of forensic evidence. Covering crime scene practical as well as forensic genetic aspects, we introduce operational requirements and lay out possible procedures, including forensic RNA analysis, when searching for, collecting, analyzing, and contextualizing such trace material. We discuss the intricacies and rationales of ballistic model building, employing different tissue, skin, and bone simulants and the advantages of the “triple-contrast” method in molecular ballistics and give advice on how to stage experimental shootings in molecular ballistic research. Finally, we take a look at future applications and prospects of molecular ballistics.

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.

Ballistic gelatine-what we see and what we get

Since decades, 10% gelatine is used to visualize and estimate the energy transfer of projectiles. The study performed investigates the correlation of the temporary cavity (TC) recorded by high-speed video (HSV) and the cracks in gelatine slices. A total of 36 shots were performed from distance using form-stable bullets (FMJ), 12 using deforming bullets (HP) in the calibres .32 auto, .38 special and 9 mm Luger. The target models were prepared according to Fackler's standard as 10% gelatine cubes with 12 cm edge length doped with a paint pad beneath the front cover ("reference cube"). Scaled images of the TC were recorded with 40.000 fps. The cubes were cut into 1-cm-thick gelatine cross sections, which were scanned. The evaluation of the destruction (cracks) was performed by the mean of image analysis measuring the longest crack, the wound profile according to Fackler and applying the polygon method. The height of the TC was measured each cm along the bullet path. The energy deposited ranged between 54 and 269 J. FMJ caused tubular, HP provoked pear-like TC. The tubular aspect was consistent with the quasi-constant deceleration of FMJ; however, the pear-like TC did not metrically represent the deceleration of HP. The profiles of destruction parameters were convex for both projectile types and did not match the profile of bullet deceleration. The maximum of TC stretching observed in HSV did not coincide with maximum gelatine destruction (crack lengths). The total energy transfer correlated with all considered destruction parameters in their sum; however, the cross-sectional parameters did not reflect the energy transfer per centimetre bullet path. The sum of the TC's heights correlated with the energy deposited, but differently for FMJ and HP. Obviously, the 12-cm reference cube reflects the energy transfer by a bullet as a whole.