Remington 870 Fieldmaster Black 20 Gauge 3in Pump Action Shotgun - 21in - If the Model 870 were introduced today, it would be hailed as a major advance in pump-action shotgun design - the ultimate in strength, durability, silky-smooth bind-free action, and sleek classical lines. Yet this remarkable shotgun has been around for more than half a century, and has become the best-selling shotgun of any type in history, with over 11 million made.