The Sweeper 12 gauge is a 12 gauge shotgun in Syphon Filter: The Omega Strain, Dark Mirror and Logan's Shadow.
"The Sweeper is a lethal riot control device designed to take out a crowd of hostile individuals very quickly. It has an 8-round cartridge that is easy and quick to replace. All the user has to do to take out a rioting crowd is hold the trigger and sweep across the crowd. After a few seconds most individuals will flee the scene or be incapacitated. Due to its lethality and changing times, this weapon is no longer considered for riot control and is likely to turn up in the hands of any organised criminals or terrorists."
-Description from Omega Strain
Syphon Filter: The Omega Strain
The Sweeper is unlocked by gaining the South American Freedom Medal. It is great due to the 8-round magazine size but needs the player to complete objectives late into the game if one wants this weapon. It is good in Carthage 1, Carthage 2 as well as Tokyo due to enemies in these levels using the same ammunition.
Syphon Filter: Dark Mirror
The weapon is seen during Episodes 6 and 7, mostly used by Red Section thugs. It is devastating at close range but becomes useless over a distance.
Syphon Filter: Logan's Shadow
The weapon can be used during Episode 6, where a crate near the crane contains it, but is not seen in enemy hands.