SHOTGUN: MOSSBERG MODEL 510 MINI PUMP, SERIAL NUMBER U250942, BLUE, CASE NOT INCLUDED, PUMP, 20 GAUGE, 18 Notes: MOSSBERG 510 MINI PUMP, 12ga, 18" barrel, 4+1 The Mossberg 510 Mini Pump is a compact pump-action shotgun designed with a shortened, lightweight configuration. It features a practical pump-action mechanism, synthetic construction, and a compact overall profile. Specific specifications such as gauge, chambering, barrel length, and stock configuration may vary by individual model.