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How a Walther MPL SMG works
The Walther MP (Maschinenpistole) series is a family of 9×19mm Parabellum submachine guns produced in West Germany from 1963 to 1985 by Walther.
The mechanism is simple blowback, but with an unusual bolt design, wherein most of the mass of the bolt consists of a hollow tubular weight that is actually placed above and parallel to the barrel, housed in a separate channel in which it reciprocates when the gun is fired. Fixed rigidly to the underside of this heavy tube is an additional steel block that performs most of the tasks of a standard sub-machine gun bolt, that is, this part chambers the bullets and seals them in the chamber, fires them and extracts the empty cartridges. This section is however very small and light in comparison to the bolts of more conventional simple blowback sub-machine guns, as most of the necessary mass and thus inertia is provided by the tubular weight above. This weight extends well ahead of the chamber when the gun is in battery, and also contains the main spring, and so the design is horizontally compact and permits both guns to feature relatively long barrels for their overall length. The receiver is made from stamped steel, with plentiful ventilation slots; and the prominent cocking handle is located on its left front. A selective fire switch is also on both the left and right side of the receiver, behind the trigger, allowing for ambidextrous use.