Experimental and numerical study of blood backspatter interaction with firearm propellant gases

Experiments are used to quantify the influence of propellant gases on blood backspatter and the numerical model presented in the first part of this work (G. Li, N. Sliefert, J. B. Michael, A. L. Yarin, Phys. Fluids, 33, 043318 (2021)) is compared with the experimental results, which stem from muzzle gas expansion. Experimental results with blood backspatter show the reversal of backspatter blood drops and also indicate the presence of secondary atomization induced by the high relative velocity of the oncoming muzzle gases and the backward propagating bullet-induced blood spatter. To characterize the degree of influence, the muzzle gases for a range of modified and unmodified rifle and pistol configurations are considered. These muzzle gas expansions are used to infer the parameters of the numerical model presented in the first part. The significant effects of muzzle gases on blood backspatter have important implications for the use of forensic analysis of deposited bloodstain patterns, where flow reversal and breakup may significantly alter the forensic evidence.