The Mossberg 500 is a shotgun manufactured by O.F. Mossberg & Sons.
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A Mossberg 500

Rather than a single model, the 500 is really a series of widely varying hammerless, pump action repeaters, all of which share the same basic receiver and action, but differ in bore size, barrel length, choke options, magazine capacity, and "furniture" (stock and forearm) materials. Other model numbers included in the 500 series are the 590, 505, and 535.