The M1S stands for 'Mark 1 Submachine Gun'. A magazine fed rubber band gun allow the user to reload the gun just by switching the magazine.

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The mechanism of the M1S is from the Magarm-2 By Parabellum Arm. it only have 5 moving parts, 2 from the magazine and 3 from the receiver.

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The M1S is a fully automatic only gun to keep the mechanism simple.