In a gun tube for firing rounds of smart ammunition, a sensor means applied to the ammunition which enables the calculation of muzzle velocity in the instant as the ammunition leaves the muzzle edge of the gun tube. The sensor relies on measurement of magnetic field induced voltages which are unique as the ammunition leaves the muzzle edge of the gun tube. Each round of ammunition has a planar transformer of wiring applied longitudinally on the side of the round, which aids in creating the necessary magnetic fields.