Brain Response to Overpressure and Recoil Loads from Discharge of Long-Range Precision Rifle

Abstract

The presence of concussion-like symptoms related to overpressure exposure and recoil forces from long-range precision rifle (LPR) training has been reported in the literature. However, the recoil head kinematics, overpressure loadings from LPR discharge, and the interaction of the two load paths have not been previously quantified. In the present study, experiments were undertaken by the Defense Research and Development Canada (DRDC) Valcartier Research Centre, using an instrumented head form to measure the overpressure from LPR discharges and to measure head kinematics resulting from recoil using instrumented mouthguards on human volunteers. The measurements included a high-speed video to enable estimation of the relative onset timings of overpressure and recoil head kinematics. The LPR configurations encompassed both muzzle suppressor and non-suppressor configurations. Then, planar finite element (FE) head models (in the sagittal and transverse planes) were used to quantify the effects of the measured loadings on the brain response. The models were used to simulate three boundary conditions: only the overpressure, only the recoil head kinematics, and combining the two loadings to investigate the interaction of the load paths. The overpressure resulting from discharge of the LPR was reduced significantly when the suppressor configuration was employed. The overpressure reached the head 3.6 ms after exiting the barrel of the LPR, with peaks ranging from 0.2 to 27.6 kPa with and without suppressor, respectively. The onset of recoil head kinematics varied between operators, occurring between 7.4 to 24.4 ms after the onset of overpressure loading to the head. In addition, the FE models showed that the intracranial pressure response predicted in the head demonstrated an interaction between overpressure and head kinematics, while strain in the brain was largely governed by recoil head kinematics. The results of this study provide important information regarding the relative severities and interaction between the overpressure and recoil head kinematics in LPR operators.