An Ignored Mechanism for the Longitudinal Recoil Force in Railguns and   Revitalization of the Riemann Force Law
  The electric induction force due to a time-varying current is used to account for the longitudinal recoil force exerted on the rails of railgun accelerators. As observed in the experiments, this induction force is longitudinal to the rails and can be the strongest at the heads of the rails. Besides, for the force due to a closed circuit, it is shown that the Riemann force law, which is based on a potential energy depending on a relative speed and is in accord with Newton's law of action and reaction, can reduce to the Lorentz force law. 
Ching-Chuan Su