After firing, gas pressure served to unlock the breech, while barrel recoil was used to cycle the action (eject spent cartridge and load a fresh one).
To counteract this weakness, HE ammunition with a reduced load of propellant was used, resulting in a loss of about 100 m/s in muzzle velocity compared to the MK 101, but the rate of fire was increased.
The MK 103 entered service in 1943 as the main armament of the Hs 129 B-1 ground-attack/tank-destroyer aircraft, mounted on the underside of the fuselage in a conformal gun pod.
If mounted elsewhere, such as in the wing, the asymmetric force of the cannon's recoil tended to yaw the aircraft's nose to one side.
A modified version with a reduced-profile barrel, the MK 103M, was developed and possibly tested for use as a Motorkanone cannon on single-engine fighter planes such as the Bf 109K, but probably never saw active service.