In this paper we present a theoretical study of a 80 mm round bore railgun which allows us, by a current distribution along the projectile, to accelerate a long rod penetrator with a fineness ratio of 30 up to a muzzle velocity of 2500 m/s with an overall efficiency greater than 30 %.This study was started because an optimal impact velocity which allows a given depth of penetration to be reached with a minimum kinetic energy exists for all the targets (homogeneous, composite, structured or reactive). Two years ago we showed that this impact velocity is always greater than 2300 m/s for a heavy alloy penetrator with L = 30. For these velocities the electromagnetic rail launchers may have efficiencies over 35 % when classical powder guns have efficiencies about 20 %.