 58 is a selective fire gas-operated weapon that bleeds expanding combustion gases generated in the barrel from the ignited cartridge through a port drilled in the barrel, from the chamber, opening into a hollow cylinder located above the barrel that contains a short-stroke piston.The vz.58 does not have a gas regulator and the full force of the gas pressure is exerted on the piston head, propelling it backwards in a single impulsive blow.