The systemic error in the vertical component of handgun bullet trajectory reconstructions.

Establishing the path or trajectory of a fired bullet is an often recurring part of shooting incident reconstruction. The current study describes how gravitational pull causes a systemic error on the vertical component of a trajectory reconstruction. Bullet drop, drop angle, and vertical offset are explained and calculated for 10 different handgun/ammunition combinations over a range of distances up to 100 m. The presented results are intended to provide forensic firearm examiners with a reference frame for the magnitude of error introduced on handgun bullet trajectory reconstructions over distance. Threshold values of 20 and 30 m are proposed as conservative distances up to where bullet trajectories can be modeled as straight lines with subsonic/transonic handgun bullets and with supersonic handgun bullets respectively. Both the bullet drop and vertical offset will be below 5 cm at these distances for those categories. The drop angle will be below 0.3°.

The relationship between pellet size and shotgun dispersion patterns.

When reconstructing a shooting incident with a shotgun, the muzzle-to-target distance can be determined by relating the size of a dispersion pattern found on a crime scene to that of test shots. Ideally, the test shots are performed with the weapon and ammunition that were used in the incident. But sometimes examiners will have to resort to alternatives, such as using cartridges of the same brand and type but with another pellet size. For this reason, the relationship between pellet size and shotgun dispersion patterns was studied with both lead and steel shotgun pellets. Cartridges were loaded with identical cartridge cases, powder charges, and wads but with different pellet sizes, below size B. The cartridges were fired, and the dispersion patterns at 5 m in front of the muzzle were measured and compared. The results provide strong support for the proposition that shotgun dispersion patterns with both lead and steel shot increase with decreasing pellet size if all other relevant parameters are kept equal. The results also provide an indicative measure of the magnitude of the effect. Pattern sizes were approximately 1.7 times larger with #9 than with #0 lead shot and 1.4 times larger with #9 than with #1 steel shot. The differences between consecutive shot sizes were generally smaller. This means that cartridges of equal brand and type but with the next nearest shot number can be used for a muzzle-to-target distance determination, keeping the information of the current study in mind in the final interpretation of the results.

Gunshot trauma in human long bones: towards practical diagnostic guidance for forensic anthropologists.

In contrast to cranial gunshot trauma, diagnosis and interpretation of gunshot trauma to long bones remains difficult and controversial. The aim of this study is to review the published literature on fracture patterns resulting from gunshot trauma in human long bones, and to use the described characteristics to provide practical guidance for the forensic anthropologist. In order to achieve this, medical and forensic publications on this topic were reviewed. Several types of fractures, such as linear, oblique, comminuted and butterfly fractures, have been observed in either the shaft or the ends of long bones. Indirect fractures that are not caused by bullets striking bone directly but by bullet-induced forces to the surrounding soft tissue have been found as well. Some of these fractures are related to a specific context or mechanism which might help in the forensic reconstruction of events. It is recommended that future research should focus on available medical data to provide more detailed descriptions on fracture patterns for forensic purposes. Experimentation with bone surrogates and computer modelling might also provide better and more realistic reconstructions of gunshot trauma in the future and provide valuable insights for its diagnosis and interpretation in forensic anthropology.

Influence of Muzzle Instability on Bullet Deflection after Perforating Laminated Particleboards.

The influence of muzzle instability on bullet deflection, when perforating laminated particleboards, was studied with three different handgun bullet types. The mean deflection angles of .32 Auto FMJ and .38 Special SJHP bullets were calculated to be 0.90° and 0.83°, respectively after perforating particleboards orthogonally at a 1 m muzzle-to-target distance. The mean angles dropped to 0.70° and 0.58° at a 15 m muzzle-to-target distance. The differences in deflection angles proved to be statistically significant (p < 0.05) with p-values of 0.023 and 0.001, respectively. The mean calculated deflection angles of .38 Special LRN bullets also dropped from 1.51° to 1.38° when the muzzle-to-target distance was increased from 1 to 15 m, but this difference was not significant (p-value of 0.357). The results support the hypothesis that muzzle instability has an influence on deflection. The possible implications for shooting incident reconstructions and for future research are discussed.

Magazine Influence on Cartridge Case Ejection Patterns with Glock Pistols.

In this study, the cartridge case ejection patterns of six different Glock model pistols (one specimen per model) were compared under three conditions: firing with a loaded magazine, an empty magazine, and without magazine. The distances, covered by the ejected cartridge cases given these three conditions, were compared for each of the six models. A significant difference was found between the groups of data for each of the tested specimens. This indicates that it is important that, to reconstruct a shooting scene incident based on the ejection patterns of a pistol, test shots are fired with the same pistol type and under the correct magazine condition.

Bullet Trajectory after Impact on Laminated Particle Board.

When reconstructing a bullet's trajectory prior to impact using the spatial orientation between two consecutive bullet defects (e.g., by probing), it is important to take the bullet's deflection into account. The (critical) ricochet angles as well as the vertical and horizontal deflection angles of eight cartridge types on laminated particle board have been studied. For all eight of the cartridge types combined, the critical ricochet angles lie between approximately 14° and 26°, while for the subgroup of the jacketed bullets, this range lies lower, between approximately 14° and 18°. The data from this study can be used to assess the accuracy and precision of the applied method. The results show that the highest deflection angles are seen near the critical ricochet angle. Generally speaking, vertical and horizontal deflection angles can almost be neglected above angles of incidence of 30° or 40° for handgun ammunition when shooting at laminated particle board.

Possible influences on bullet trajectory deflection in ballistic gelatine.

The influence of the distance to the top and bottom of a gelatine block and to bullet tracks from previously fired shots on a bullet's trajectory, when passing through ballistic gelatine, was studied. No significant difference in deflection was found when trajectories of 9mm Luger bullets, fired at a 3.5cm distance to the top and bottom of a gelatine block and to bullet tracks from previously fired shots, were compared to trajectories of bullets fired 7cm or more away from any of the aforementioned aspects. A surprisingly consistent 6.5° absolute deflection angle was found when these bullets passed through 22.5 to 23.5cm of ballistic gelatine. The projection angle, determined by the direction of the deflection, appeared to be random. The consistent absolute angle, in combination with the random projection angle, resulted in a cone-like deflection pattern.

Bullet trajectory reconstruction - Methods, accuracy and precision.

Based on the spatial relation between a primary and secondary bullet defect or on the shape and dimensions of the primary bullet defect, a bullet's trajectory prior to impact can be estimated for a shooting scene reconstruction. The accuracy and precision of the estimated trajectories will vary depending on variables such as, the applied method of reconstruction, the (true) angle of incidence, the properties of the target material and the properties of the bullet upon impact. This study focused on the accuracy and precision of estimated bullet trajectories when different variants of the probing method, ellipse method, and lead-in method are applied on bullet defects resulting from shots at various angles of incidence on drywall, MDF and sheet metal. The results show that in most situations the best performance (accuracy and precision) is seen when the probing method is applied. Only for the lowest angles of incidence the performance was better when either the ellipse or lead-in method was applied. The data provided in this paper can be used to select the appropriate method(s) for reconstruction and to correct for systematic errors (accuracy) and to provide a value of the precision, by means of a confidence interval of the specific measurement.

The Influence of Wood Grain on the Bullet's Ricochet Behavior.

When a bullet ricochets from wood, various parameters will influence its behavior. In this study, the influence of the wood grain on the ricochet angle (ß) and deflection angle (γ) is assessed. Series of five .32 Auto bullets were fired at different angles of incidence (α) on boards of six wood types. The results confirm the previously shown effect that the mean ß-angles usually exceed α and increase when α increases. Overall, the maximum mean γ occurs when the angle of wood grain (ζ), in relation to the plane of impact, lies between 30° and 75° but differs per combination of wood and α. The results show the inclination of γ toward the left or right, depending on the bullets left or right rotation while also showing that the direction of ζ can enhance or counteract this effect considerably, especially when α is close to the critical ricochet angle.

Influence of Running on Pistol Shot Hit Patterns.

In shooting scene reconstructions, risk assessment of the situation can be important for the legal system. Shooting accuracy and precision, and thus risk assessment, might be correlated with the shooter's physical movement and experience. The hit patterns of inexperienced and experienced shooters, while shooting stationary (10 shots) and in running motion (10 shots) with a semi-automatic pistol, were compared visually (with confidence ellipses) and statistically. The results show a significant difference in precision (circumference of the hit patterns) between stationary shots and shots fired in motion for both inexperienced and experienced shooters. The decrease in precision for all shooters was significantly larger in the y-direction than in the x-direction. The precision of the experienced shooters is overall better than that of the inexperienced shooters. No significant change in accuracy (shift in the hit pattern center) between stationary shots and shots fired in motion can be seen for all shooters.

An empirical study on the relation between the critical angle for bullet ricochet and the properties of wood.

The properties of a bullet, an object, and the incidence angle determine whether the bullet will penetrate, perforate, or ricochet. In this study, the critical angle for ricochet was established for .32 Auto and 9 mm Luger bullets on Abachi, Southern Yellow Pine, Beech, and Ipe wooden boards. Results show that the critical angle differs depending on caliber and wood type. The critical angle is higher for .32 Auto bullets than for 9 mm Luger bullets and increases with increasing wood density and Janka hardness. The established critical angles for ricochet on the lightest and softest wood (Abachi) are 10.4° and 10.3° for .32 Auto and 9 mm Luger, respectively. For the heaviest and hardest wood (Ipe), the angles were 45.0° and 33.4°, respectively. The combined results on the four tested woods show a strong linear relationship between both the density and the hardness and the critical angle for both calibers.