The M78, and the rifles on which it is based, the M62 and M76, are updates of the venerable AK-47 design. Starting with a licensed version of the AK-47 receiver, Valmet set about upgrading the design at every point. Tolerances are tighter than the Soviet bloc AKs while still being generous enough to assure reliability in all climates. The gas piston included small "fingers" near the piston to ensure smoother functioning inside the gas tube, which helped to increase the inherent accuracy of the rifle. Another move toward increased accuracy was the upgraded sights.