1. GAS SYSTEM
a round is in the chamber; the breech block is locked; the shot has just been fired.
— The bullet moves along the barrel and reaches the level of the gas port (f) (fig. 4).
— The combustion gases pass through the gas port (f) and reach the gas plug (a), which closes the front end of the gas cylinder, screwed into the gas block (b); if the gas plug is closed (Jetters Gr showing on top), the gas intake is blocked and the weapon will then function as a repeating rifle.
— If the gas pJug is open (letter A showing on top), gas passes through the plug (a) and neaches the piston head (d).
— Under pressure of the combustion gases, the piston moves backward and uncovers the gas outlet vent (e).
— The gas exhaust vent is partially closed by the gas regulator (c) the position of which determines the gas exhaust and thus controls the quantity of gas acting on the piston. The position of the gas regulator sleeve is normally determined when the weapon is fired for gas regulator setting (see Chapter IV).
— As the piston (P) moves back words, it contacts the slide (B) (fig. 5), thrusting it to the rear.
— The piston spring, which has been compressed by the rear movement of the piston, relaxes and returns the piston to its forward position.
2. REAR MOVEMENT OF THE MECHANISM
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