Mossberg 75771 SA-20 All Purpose Field 20 Gauge with 28" Vent Rib Barrel, 3" Chamber, 4+1 Capacity, Matte Blued Metal Finish & Black Synthetic Stock Right Hand (Full Size) Includes 5 Sport-Set Chokes. Mossberg's SA-20 uses a smooth cycling, gas-operated system for a lightweight, soft-shooting shotgun perfect for both hunting and target shooting. This All Purpose Field model has a black synthetic stock with a 14" LOP, 28" vent rib barrel with a matte blued metal finish, and a metal bead front sight. It includes Mossberg International's Sport Set of 5 choke tubes.