An electromagnetic railgun having a layer of low conductivity material along the rails to interface with the armature as the armature is propelled along the rails. The low conductivity material has been found to permit rapid current penetration between the layer and armature, thereby inhibiting undersirable high current density formation along the trailing edge of the armature. Advantageously, inhibiting the high current density formation permits use of a solid armature at velocities exceeding on kilometer per second. Preferably, the layer is composed of graphite or a graphite/copper mixture. A layer of copper or other high conductivity material is preferably laminated to the low conductivity graphite layer to reduce the overall railgun circuit resistance. In the preferred embodiment, the layer of low conductivity material increases in thickness from the breech to the muzzle to decrease railgun circuit resistance.