A fluid percussion system for modeling penetrating brain injury includes a fluid percussion device that takes inputs in the form of pressurized gas and electrical signals from a computer and outputs a single hydraulic pulse, or multiple hydraulic pulses in quick succession. The fluid percussion device may include a pneumatic cylinder assembly and a hydraulic cylinder assembly that is actuated by the pneumatic cylinder assembly to produce the hydraulic pulse(s) of pressurized fluid. Each pulse may be used to rapidly inflate and deflate an attached balloon (representing a brain penetrating device). The balloon may be inserted in a test specimen, and the rapid inflation and deflation of the balloon creates a lesion that simulates a penetrating brain injury. A calibration system that employs an optical sensor may be used to determine maximum balloon diameter achieved during rapid inflation.