Theoretical and experimental investigation of forward spatter of blood from a gunshot

A theoretical model predicting forward blood spatter patterns resulting from a round nose bullet gunshot wound is proposed. The chaotic disintegration of a blood layer located ahead and aside of the bullet is considered in the framework of percolation theory. The size distribution of blood drops is determined, which allows for the prediction of a blood spatter cloud being ejected from the rear side of the target where the bullet exits. Then, droplet trajectories are numerically predicted accounting for gravity and air drag, which is affected by the collective aerodynamic interaction of drops through air. The model predicts the number and area of individual stains, as well as the stain distribution as a function of distance from the region of origin. The theoretical predictions are compared with experimental data acquired in this work from 9 mm Luger copper full metal jacket bullets fired from a handgun. The agreement between the predicted and experimentally measured parameters is found to be good.

Figure 1

Schematic of the forward spatter experimental setup. The muzzle of the gun was located 304.8 cm away from the target, which was impacted by the bullet normally at 152.4 cm above the ground. The bullet completely perforated the target to produce a forward spatter pattern on the horizontally laid butcher paper substrate behind the target. The target thickness was 5 mm and the radius of the bullet was 4.5 mm.

Figure 2

Schematic of the coordinates and variables used in the theoretical model.

Figure 3

Target discretization types from the bullet as it travels from the right to the left. The gray cross-hatched section represents the portion of the target in which droplets form and are ejected from the target. (a) Section of the target where $V_T$ is approximated as a cone, and (b) where $V_T$ is approximated as a cylinder.

Figure 4

Schematic of the discretization of the paper substrate. The dashed lines are where the locations of the data points, both theoretical and experimental, are accounted for.

Figure 5

A 9 mm Luger copper full metal jacket bullet and cartridge casing used in the experiment with the ovoid of Rankine shown by the line superimposed on its leading edge.

Figure 6

The dependence of the droplet tail detachment time on its characteristic size used in the simulations in conjunction with Eq. (44).

Figure 7

The number of stains deposited on the floor vs the distance from the rear side of the target in forward blood spatter. The red circles correspond to the predicted results, and the blue squares to the experimental data. It should be emphasized that these data correspond to the combined results of five experiments as discussed in Sec. 2.

Figure 8

Schematic of stain formation due to a blood droplet impacting onto a horizontal surface.

Figure 9

The average stain area as a function of distance from the rear side of the target in forward blood spatter. The red circles depict the predictions and the blue squares are the experimental data. The error bars for the experimental data indicate the standard deviation in the stain area arising from the five experiments.