Mossberg SA-20, Compact, Semi-automatic Shotgun, 20 Gauge, 3 Chamber, 24 Barrel, Sport Set (5 Total) Chokes, Black Finish, Black Stock, Bead FO Sights, 4Rd 75770 The Mossberg SA-20 is a lightweight, soft shooting 20 gauge sporting shotgun that is perfect for both hunting and target shooting. The SA-20 has a smooth cycling semi-automatic gas operated system.