consistency in shot peening is obtained by a system using a force sensor to sense the reaction force from a shot peening gun . the reaction force is used to calculate the average velocity of the shot stream . since the quality of effect of the shot peening process depends upon the square of the velocity of the shot and the mass of the shot , control of the shot velocity and mass flow rate is used to provide consistent shot peening results . additionally , the force sensor is used to trigger an alarm and / or turn off the shot peening if the reaction force is too low such that a clogged nozzle or other malfunction is occurring .