Mossberg 590M Mag-Fed Professional Series 12-gauge shotgun. 
 
This specific model (MFG# 50220) is characterized by its high-visibility safety orange synthetic stock and is often designated for professional or "less-lethal" applications. 
 
Key Specifications
Model: 
Mossberg 590M Professional (Mag-Fed)
Gauge: 12 Gauge.
Action: Pump-Action.
Capacity: 10+1 rounds (includes one 10-round detachable magazine).
Barrel: 18.5-inch heavy-walled barrel with a Tungsten Gray Cerakote finish.
Sights: Ghost Ring rear sight and Fiber Optic front sight.
Stock: Magpul SGA Safety Orange Synthetic Stock.
Chamber: 2.75 inches.