Factory Remington 870 Express 20 Gauge Fully Rifled Slug Barrel. This will not fit the older 20 gauges built on the 12 gauge frame. 20 inches longbr Handles both 2 3/4 and 3 inch shellsbr Will work on 870 Express or Wingmasterbr Matte Finish. Rifle Sights. This will not fit the older 20 gauges built on the 12 gauge frame.