Mossberg 590A1, Special Purpose, Pump Action, 12 Gauge, 3 Chamber, 20 Heavy Wall Barrel, Parkerized Finish, Synthetic Stock, Bead Sight, 8Rd 51660 Selected by the U.S. armed forces after passing the rigors of MilSpec qualification, the 590A1 is the duty shotgun of choice for military and law enforcement agencies worldwide. 590A1 models offer a variety of sighting options to meet mission-specific needs.