The Mossberg 590M is a pump-action, magazine-fed shotgun featuring a detachable double-stack magazine and a heavy-walled barrel. Specifications vary by model. 590M Mag-Fed +1 Gun-shop listing details Manufacturer: Mossberg Model: 590M Action: Pump-action Gauge: 12 gauge Chamber: 2 3/4-inch shells Barrel length: 18.5 inches on standard models Magazine capacity: 10 rounds; 10+1 total on standard models Magazine type: Detachable, double-stack Overall length: Approximately 39.5 inches on the original standard model Stock: Black synthetic on standard models Sights: Bead sight on the base model Finish: Matte blue on original standard models Approximate weight: 7.75 lbs on the original standard model