The MK1 series is a significant product improvement for the M4/M16-type carbines and rifles. Utilizing the PWS proven long stroke piston system, the MK1 series greatly reduces fouling in the action of the weapon making it as reliable as the AK47 that it was designed after. The PWS proprietary operating system utilizes an operating rod that is attached to the carrier and a floating head piston that is attached to the operating rod. There are no unnecessary gas adjustments and only one moving assembly.