A projectile or an armour plate can be accelerated by use of only electric energy in a coilgun. If the projectile only has a flat metallic surface facing the accelerating coil, eddy currents will be induced in the projectile during the acceleration and the force action between projectile and stator is determined by the magnetic field from the stator coil. By using a current carrying coil in the projectile, the force action will be between two repelling electromagnets. The report presents an investigation of the efficiency for conversion between electrically supplied energy and the projectile kinetic energy immediately after the acceleration for the two cases with passive and active current path in the projectile. Efficiencies reached are in the range 3 - 7 % with the higher values obtained for higher supplied electric energies. For current pulses with duration of about 0.8 ms, the passive current path seems to be more efficient, while pulse durations of about 1.5 ms show a higher efficiency for the projectile with an active current path in a coil. The electric energy transfer to the projectile coil exhibits problems with resistive losses in the sliding contacts and an increased friction between sliding contacts and the projectile due to thermal effects. In spite of this, the concept with an active current path in the projectile is still interesting. The report concludes with suggestions for extended studies of electromagnetic acceleration.