Complex sentence: This meant it could be fired in fully automatic mode in a receiver that weighed closer to that of a standard rifle than a machinegun, yet still had much greater velocity and stopping power than the 9 mm Parabellum, which was the standard for German submachine guns.
Split into simpler sentences: This meant it could be fired in fully automatic mode by a receiver that weighed closer to that of a standard rifle than a machinegun. However, the round was in a rifle cartridge and thus was able to be fired with much greater velocity than the 9 mm Parabellum which was the standard for German submachine guns.