A railgun's a purely electrical gun that accelerates a conductive projectile along a pair of metal rails using the same principles as the homopolar motor. Railguns use two sliding or rolling contacts that permit a large electric current to pass through the projectile. This current interacts with the strong magnetic fields generated by the rails and this accelerates the projectile. The U.S. Navy has tested a railgun that accelerates a 7 pound projectile to seven times the speed of sound. Railgu… (More on Railgun)