 The operating mechanism differed from the recoil-operated MK 101 in that it used a combination of gas and recoil operation.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).Because of a combination of lower grade steels and lighter components, the mechanism of the MK 103 was not as strong as the MK 101.