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.