The 870 Marine Magnum in 20 gauge applies the full electroless nickel plating to the lighter platform. Popular for coastal small-boat use and saltwater environments where a 12-gauge is heavier than necessary. The 20-gauge Marine Magnum is one of the rarest 870 variants in production. Type: Shotgun Action: Pump-Action Caliber: 20 Gauge Capacity: 5 Year introduced: 2005, USA Weight: 160 oz Overall length: 38" Status: Active Intended use: Maritime, Home Defense