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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.

From time to time, severe or fatal injuries caused by small caliber air rifle projectiles are seen. In forensic sciences, the theoretical wounding potential of these weapons and projectiles is widely known. Usually, shots against the skull were reported and, in these cases, penetrating the eyes or thin bone layers of the temporal region. Amongst a huge number of different projectiles available for air guns, sub-caliber 4.4-mm (.173) caliber steel ball projectiles were used in an unusual suicide case. This case led to fundamental questions concerning wound ballistics. An 82-year-old man shot once against his right temporal region and twice into his mouth with a 4.5-mm (.177) caliber air rifle. Because of the exceptionally deep penetration of the base of the skull and the use of spherical-shaped sub-caliber air rifle projectiles, terminal ballistic features were analyzed and compared to results published in forensic literature. Test shots using the same weapon and similar projectiles were fired into ballistic gelatin to measure and calculate basic wound ballistic variables of cal. 4.4-mm (.173) steel balls. In comparison, further test shots with cal. 4.5-mm (.177) steel balls BB (ball bearing), flat-headed and pointed air rifle pellets ("diabolos") were carried out. The theoretical penetration depth in solid bone was calculated with 36.4 mm, and test shots in gelatin from hard contact produced an on-average wound track of 120 mm underlining the potential wounding effect. Furthermore, spherical projectiles could roll back and forth within the barrel, and an air cushion between projectile and breechblock can reduce muzzle velocity by more than half, explaining the retained missile in the temporal region.

Amongst hundreds of different projectiles for air guns available on the market, hollow-point air gun pellets are of special interest. These pellets are characterized by a tip or a hollowed-out shape in their tip which, when fired, makes the projectiles expand to an increased diameter upon entering the target medium. This results in an increase in release of energy which, in turn, has the potential to cause more serious injuries than non-hollow-point projectiles. To the best of the authors’ knowledge, reliable data on the terminal ballistic features of hollow-point air gun projectiles compared to standard diabolo pellets have not yet been published in the forensic literature. The terminal ballistic performance (energy-dependent expansion and penetration) of four different types of .177 caliber hollow-point pellets discharged at kinetic energy levels from approximately 3 J up to 30 J into water, ordnance gelatin, and ordnance gelatin covered with natural chamois as a skin simulant was the subject of this investigation. Energy-dependent expansion of the tested hollow-point pellets was observed after being shot into all investigated target media. While some hollow-point pellets require a minimum kinetic energy of approximately 10 J for sufficient expansion, there are also hollow-point pellets which expand at kinetic energy levels of less than 5 J. The ratio of expansion (RE, calculated by the cross-sectional area (A) after impact divided by the cross-sectional area (A 0) of the undeformed pellet) of hollow-point air gun pellets reached values up of to 2.2. The extent of expansion relates to the kinetic energy of the projectile with a peak for pellet expansion at the 15 to 20 J range. To conclude, this work demonstrates that the hollow-point principle, i.e., the design-related enlargement of the projectiles’ frontal area upon impact into a medium, does work in air guns as claimed by the manufacturers.

In medico-legal literature, only a small number of publications deal with lethal injuries caused by shots with modified guns. This might lead to the conclusion that such cases are extremely rare. However, there are cases again and yet again. During the investigation process, the modified gun is of particular importance since it can show an unusual ballistic behaviour. The present paper reports on a suicide of a 60-year-old man, committed with a modified revolver and a lead bullet. The man had a single gunshot wound with entrance at the right temporal bone. Autopsy revealed that the bullet had fragmented into two major parts. The smaller one stood outside the cranial cavity and pushed its way alongside between the cranial bone and scalp to its end position in the left temporal area. The bigger part entered the cranial cavity and ended in the left parietal lobe. In shots on ballistic soap and on a head-model, the ballistics of the weapon and lead bullet were characterized. The angle necessary for bullet fragmentation was determined by shots on ballistic soap and turned out to be 55°-60° at a velocity of around 200 m/s. This knowledge was transferred to contact shots on a head-model consisting of a layered polyurethane sphere filled with 10 % ballistic gelatine and covered with a skin-like cap almost all around. The resulting injury pattern corresponded to the one of the suicide person. The bigger bullet part entered the skull while the smaller part pushed its way alongside between skin and skull causing an outer contour shot. Furthermore, the revolver was documented firing off two bullets by one trigger pull-a phenomenon of importance for forensic casework the authors have not found reported in forensic literature.

Blocks of gelatine are used in both lethality and survivability studies for broadly the same reason, i.e. comparison of ammunition effects using a material that it is assumed represents (some part of) the human body. The gelatine is used to visualise the temporary and permanent wound profiles; elements of which are recognised as providing a reasonable approximation to wounding in humans. One set of researchers aim to improve the lethality of the projectile, and the other to understand the effects of the projectile on the body to improve survivability. Research areas that use gelatine blocks are diverse and include ammunition designers, the medical and forensics communities and designers of ballistic protective equipment (including body armour). This paper aims to provide an overarching review of the use of gelatine for wound ballistics studies; it is not intended to provide an extensive review of wound ballistics as that already exists, e.g. Legal Med 23:21–29, 2016. Key messages are that test variables, projectile type (bullet, fragmentation), impact site on the body and intermediate layers (e.g. clothing, personal protective equipment (PPE)) can affect the resulting wound profiles.

To study the question whether and how the size and position of the temporary cavity influence the morphology and especially the size of a bullet exit wound, test shots were fired to composite models consisting of gelatine and pig soft tissue covered with skin (at the exit site). The dimensions of the composite model were determined such that the exit planes were located either at the level of the narrow channel or within the temporary cavity or behind it. The chronological sequence of wound formation and its relation to the current position of the bullet were documented by means of a high-speed camera. Test shots were fired from a distance of 10 m using 5.56 × 45 mm cartridges with full metal-jacketed pointed bullets (v 0 ∼ 912 m/s, E 0 ∼ 1,663 J). The study proved that the extension and position of the temporary wound cavity was decisive for the size of the exit wound: An exit plane within the cavity resulted in particularly large skin lesions, whereas the wound diameters were much smaller if the exit plane was located in front or behind the cavity. The exit hole reaches its maximum size only after the bullet has left the target synchronous to the staggered expansion of the temporary cavity.

Hand-held pistol crossbows, which are smaller versions of conventional crossbows, have recently increased in popularity. Similar to conventional crossbows, life threatening injuries due to bolts discharged from pistol crossbows are reported in forensic and traumatological literature. While the ballistic background of conventional crossbows is comprehensively investigated, there are no investigations on the characteristic ballistic parameters (draw force, potential energy, recurve factor, kinetic energy, and efficiency) of pistol crossbows. Two hand-held pistol crossbows (Barnett Commando and Mini Cross Bow, rated draw force 362.9 N or 80 lbs) were tested. The maximum draw force was investigated using a dynamic tensile testing machine (TIRAtest 2705, TIRA GmbH). The potential energy was determined graphically by polynomial regression as area under the force-draw curve. External ballistic parameters of the bolts discharged from pistol crossbows were measured using a redundant ballistic speed measurement system (Dual-BMC 21a and Dual-LS 1000, Werner Mehl Kurzzeitmesstechnik). The average maximum draw force was 190.3 and 175.6 N for the Barnett and Mini Cross Bow, respectively. The corresponding total energy expended was 10.7 and 11 J, respectively. The recurve factor was calculated to be 0.705 and 1.044, respectively. Average bolt velocity was measured 43 up to 52 m/s. The efficiency was calculated up to 0.94. To conclude, this work provides the pending ballistic data on this special subgroup of crossbows which operate on a remarkable low kinetic energy level. Furthermore, it demonstrates that the nominal draw force pretended in the sales brochure is grossly exaggerated.

In firearm examiners’ and forensic specialists’ casework as well as in air gun proof testing, reliable measurement of the weapon’s muzzle velocity is indispensable. While there are standardized and generally accepted procedures for testing the performance of air guns, the method of seating the diabolo pellets deeper into the breech of break barrel spring-piston air guns has not found its way into standardized test procedures. The influence of pellet seating on the external ballistic parameters was investigated using ten different break barrel spring-piston air guns. Test shots were performed with the diabolo pellets seated 2 mm deeper into the breech using a pellet seater. The results were then compared to reference shots with conventionally loaded diabolo pellets. Projectile velocity was measured with a high-precision redundant ballistic speed measurement system. In eight out of ten weapons, the muzzle energy increased significantly when the pellet seater was used. The average increase in kinetic energy was 31 % (range 9–96 %). To conclude, seating the pellet even slightly deeper into the breech of spring-piston air guns might significantly alter the muzzle energy. Therefore, it is strongly recommended that this effect is taken into account when accurate and reliable measurements of air gun muzzle velocity are necessary.

In the past, the presence of textile fibres in the bullet track of gunshot injuries in body regions covered with clothes was used to differentiate between entrance and exit wounds; as with handguns, a displacement of textile fibres was considered possible only in the direction of the shot. In the present study, the transfer of textile fibres from the entrance and exit regions into the bullet path was systematically investigated with the help of a skin-gelatine composite model. For this purpose, the skin of the bullet entrance and exit region was covered with textile fabric (jeans or jersey material), before conducting four test series of ten test shots each firing a 9-mm Parabellum full-jacketed projectile from a distance of 2 m. The length of the bullet track was 25 and 8 cm, respectively. Subsequently, the bullet tracks were microscopically investigated in sections for the presence of textile fibres. In all the investigated bullet tracks, textile fibres both from the entrance and exit regions could be demonstrated. The distribution pattern depended on the length of the bullet path and the extension of the temporary cavitation. The results are discussed in relation to the relevant literature.

While the morphological appearance of injuries due to powder-actuated captive bolt stunners has been extensively investigated, medicolegal literature contains, except for one work by Nadjem and Pollak (Arch Kriminol 203:91–102), no further investigations into the physical impact characteristics of these sharp-edged circular punching tools. However, basic physical parameters, such as bolt velocity, momentum, kinetic energy, and energy density, play a crucial role in the medicolegal and traumatological assessment of captive bolt stunners and the related injuries. And also, regulatory bodies demand a reliable and repeatable measurement test set-up for the determination of captive bolt stunners’ impact characteristics. Therefore, it is the aim of this work to design and describe a test set-up based on one single photoelectric light barrier and to determine the impact parameters for a series of newly developed cal. 6.8/15 stunning devices. We found that bolt velocity ranges from v = 42 to 54 m/s, while momentum ranges from p = 11 to 14 Ns, and kinetic energy reaches values from E = 224 to 369 J. The efficiency of the captive bolt stunner, defined as the ratio of the kinetic energy of the stunner’s bolt to the potential energy of industrial blank cartridges, also described in this work for the first time, was found to vary between 36 and 46 %.

Medical literature abounds with reports on injuries and fatalities caused by airgun projectiles. While round balls or diabolo pellets have been the standard projectiles for airguns for decades, today, there are a large number of different airgun projectiles available. A very uncommon — and until now unique — discarding sabot airgun projectile (Sussex Sabo Bullet) was introduced into the market in the 1980s. The projectile, available in 0.177 (4.5 mm) and 0.22 (5.5 mm) caliber, consists of a plastic sabot cup surrounding a subcaliber copper-coated lead projectile in typical bullet shape. Following the typical principle of a discarding sabot projectile, the lightweight sabot is supposed to quickly loose velocity and to fall to the ground downrange while the bullet continues on target. These sabot-loaded projectiles are of special forensic interest due to their non-traceability and ballistic parameters. Therefore, it is the aim of this work to investigate the ballistic performance of these sabot airgun projectiles by high-speed video analyses and by measurement of the kinetic parameters of the projectile parts by a transient recording system as well as observing their physical features after being fired. While the sabot principle worked properly in high-energy airguns (E > 17 J), separation of the core projectile from the sabot cup was also observed when discharged in low-energy airguns (E

The capability of conventional air gun lead pellets (diabolo pellets) to cause severe injuries or fatalities even at low kinetic energy levels is well documented in medical literature. Modern composite hunting pellets, usually a metal core (made of steel, lead, zinc, or a zinc and aluminum alloy) encased in a plastic sleeve, are of special forensic and traumatological interest. These projectiles are advertised by the manufacturers to discharge at higher velocities than conventional air gun pellets, thus generating very high tissue-penetrating capabilities. Lack of experimental data on these uncommon air gun projectiles induced this work. Ballistic parameters of 12 different caliber .177 (4.5 mm) composite pellets, discharged from two spring-piston air guns (Weihrauch HW 35, Webley CUB) and three pneumatic air guns (Walther LGR, Walther LG400, Walther LP300), were investigated using a ballistic speed measurement system and compared to a conventional diabolo pellet (RWS Meisterkugel) as reference projectile. Although overall results were inconsistent, for some projectile–weapon combinations (particularly spring-piston air guns), a significant change of the kinetic energy (−53 up to +48 %) to the reference projectile was observed. The data provided in this work may serve as a basis for forensic investigation as well as traumatological diagnosis and treatment of injuries caused by these uncommon projectiles.

In current forensic practice, fatal injuries from black powder guns are rare events. In contact and close-range shots, the intensity of GSR deposition (soot, powder particles) is much greater than that in shots with smokeless powder ammunition. The same applies to any burning effects from the combustion gases. Besides, a wad of felt interposed between the propellant and the lead bullet may enter the wound channel. Apart from these findings seen in close-range shots, another characteristic feature results from the mostly spherical shape of the missiles causing maximum tissue damage at the entrance site. Two fatal injuries inflicted with muzzle-loading weapons are reported. In the first case, suicide was committed with a cal. 11.6 mm miniature cannon by firing a contact shot to the back of the neck. In test shots using black powder (1 and 2 g) as propellant, the mean bullet velocity measured 1 m away from the weapon was 87.11 and 146.85 m/s, respectively, corresponding to a kinetic energy of 32.49 and 92.95 J, respectively. Contact test shots to composite models consisting of ballistic soap covered by pig skin at the entrance site were evaluated by CT and revealed cone-like cavitations along the bullet path as known from spherical missiles and penetration depths up to 25 cm. The second case presented deals with a homicidal close-range shot discharged from a muzzle-loading percussion pistol cal. .44. The skin around the entrance site (root of the nose) was densely covered with blackish soot and powder particles, whereas the eyebrows and eyelashes showed singeing of the hairs. The flattened bullet and the wad had got stuck under the scalp of the occipital region. In both cases, there was a disproportionally large zone of tissue destruction in the initial parts of the wound tracks.

The yaw angle in flight of high velocity bullets has been discussed for a number of years, due to its contribution to the tumbling of the bullet in the target. Since few unclassified reports of contemporary bullets are available, we investigated the yaw angles of the bullets used in the M16A2, G3, AK-47 and AK-74 rifles by the shadowgraph technique. Our results show that bullets from military rifles tend to stabilize at less than 3 degrees within 25 m, and this angle has been thought to be insignificant in the production of gunshot wounds. Bullets from some modern small calibre high velocity rifles such as the M16A2 and the AK-74 can have quite large yaw angles in their initial flight. The results, which confirm the opinion of contemporary writers, should settle the controversy in this area of wound ballistics.

Traces of backspatter in gun barrels after homicidal or suicidal contact shots may be a valuable source of forensic evidence. Yet, a systematic investigation of the persistence and durability of DNA from biological traces in gun barrels is lacking. Our aim was to generate a realistic model to emulate blood and tissue spatters in gun barrels generated by contact gunshots at biological targets and to analyse the persistence and typability of DNA recovered from such stains. Herein, we devise and evaluate three different models for the emulation of backspatter from contact shots: a gelatine-based model with embedded blood bags, a model based on a spongious matrix soaked with blood and covered with a thin plastic membrane and a head model consisting of an acrylic half sphere filled with ballistic gelatine and with blood bags attached to the sphere under a 3-mm silicone layer. The sampling procedure for all three models: a first shot was fired with several types of guns at each model construction and subsequently a second shot was fired at a backstop. Blood samples were collected after each shot by probing the inner surface of the front and rear end of the respective gun barrel with a sterile swab. DNA was then extracted and quantified and up to 20 different short tandem repeat (STR) systems were amplified to generate DNA profiles. Although DNA quantity and STR typing results were heterogenous between the models, all models succeeded in delivering full STR profiles even after more than one shot. We conclude that biological traces in gun barrels are robust and accessible to forensic analysis and that systematic examination of the inside of gun barrels may be advisable for forensic casework.

STR-based individualisation of biological deposits on bullets after perforation of tissue, can identify the person injured or killed by a particular bullet and comparison with the firearms used can identify the weapon and thus possibly the person who did the shooting. In this study, the effect of subsequent impacts on intermediate targets such as loss of cells was investigated by amplification of mitochondrial (mt) DNA. Bovine tissue was perforated and the 9 mm Luger FMJ bullets were recovered from the bullet collector. The mt cytochrome-b (cyt-b) gene could be amplified by the polymerase chain reaction (PCR) from 14 out of 15 bullets. Examination with a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS) demonstrated the presence of minute dried tissue deposits on all bullets (n = 10) but was not able to establish preferential locations. In a series of 25 gunshots, various intermediate targets (glass, wood, car metal, gypsum board, asphalt) were perforated/ impacted following perforation of tissue and the cyt-b gene could be typed from all bullets. It is concluded that subsequent impacts on intermediate targets do not eliminate enough biological deposits to render DNA analysis impossible and that the amplification of mtDNA is a useful additional method.

Terminal ballistics concerns the science of projectile behaviour within a target and includes wound ballistics that considers what happens when a projectile strikes a living being. A number of soft tissue ballistic simulants have been used to assess the damage to tissue caused by projectiles. Standard assessment of these materials, such as ballistic soap or ordnance gelatine, requires the block to be opened or that a mould to be made to visualize the wound track. This is time consuming and may affect the accuracy of the findings especially if the block dries and alters shape during the process. Therefore, accurate numerical analysis of the permanent or temporary cavity is limited. Computed tomography (CT) potentially offers a quicker non-invasive analysis tool for this task. Four commercially purchased ballistic glycerine soap blocks were used. Each had a single firearm discharged into it from a distance of approximately 15 cm using both gunshot and shotgun projectiles. After discharge, each block was imaged by a modern 16 slice multi-detector CT scanner and analysed using 3-D reconstruction software. Using the anterior–posterior and lateral scout views and the multi-plane reconstructed images, it was possible to visualize the temporary cavity, as well as the fragmentation and dispersal pattern of the projectiles, the distance travelled and angle of dispersal within the block of each projectile or fragment. A virtual cast of the temporary cavity can be also be made. Multi-detector CT with 3-D analysis software is shown to create a reliable permanent record of the projectile path allowing rapid analysis of different firearms and projectiles.

DNA typing of cellular debris from perforating bullets was investigated following shooting experiments. A total of 14 perforating gunshots were fired into 9 calves. PCR typing of tissue fragments was done using bovine-specific primers flanking a 247 bp segment within the bovine lactoglobulin gene. Positive amplification results were obtained for all 9 hollow point (HP) and all 5 full metal jacket (FMJ) bullets. In contrast to HP bullets the smooth surfaces of the FMJ bullets did not have visible biological material, which resulted in weaker bands in the DNA analysis compared to HP bullets. Tissue seemed to accumulate at the base of the projectiles. Due to the lack of a suitable marker in bovines, only a species identification was carried out on the DNA from tissue on the bullets. The small amount of DNA extract (up to 5%) required for specification is promising for the successful application of a set of short tandem repeat (STR) systems for individualization in humans. By individualizing tissue on perforating bullets, the bullet and the victim it passed through can be linked. This can assist the investigation of gunshot deaths, especially when several persons are involved in a gun fight.

Shooting incidents are often portrayed as resulting in a sometimes violent backwards displacement of the victim. This opinion is also not infrequently held by expert witnesses. The physical force responsible for this would be momentum (mass x velocity). The physics of momentum in ballistic injury is explained in detail. The maximum momentum transferred from different small arms projectiles including large calibre rifles and a 12-gauge shotgun only results in a backwards motion of a 80 kg target body of 0.01-0.18 m/s, which is negligible compared to the velocity of a pedestrian (1-2 m/s). Furthermore, counterbalance is constantly maintained by neurophysiological reflexes. So the effect of the momentum transferred from the missile is virtually zero and there is no backwards motion of the person shot. Empirical evidence verifying these calculations can be obtained from hunting big game, from human gunshot victims and from a video documentary demonstrating the lack of any backwards motion of a person wearing body armour after hits from a centre fire rifle. So the alleged backwards hurling of a person shot is nothing but a myth which should be refuted not only because it is incorrect but also because it can result in miscarriages of justice.

Particulate matter on bullets may be used to decide which target they have passed through, and tissue fragments are the obvious candidates for study. In order to determine if recognizable tissue fragments could be found on full metal jacketed bullets, 44 such bullets were fired against anesthetized pigs and 36 were recovered. On 4 bullets fragments of tissue could be identified by routine cytological techniques. The procedure should be attempted in selected cases where it is imperative to know if a bullet has passed through tissue.