Effect of in-bore gas on railgun performance

Acceleration of a projectile in a nonevacuated railgun bore produces a series of shock waves traveling through the gas in front of the projectile which retards the projectile´s motion. A model is presented which describes the three components of this retarding force-the force required to accelerate the gas to the projectile velocity as it is entrained by the shock front, the force required to continue to accelerate previously shocked gas as the projectile accelerates, and the force required to overcome the viscous drag which arises from the interaction of the shocked gas and the gun tube. The authors address the relative contributions of the three components of the force and the significance of the retarding force when compared to the net accelerating force. The validity of the strong shock approximation for computing the retarding force is discussed