The Six 12-SD is the suppressed version of the Six 12 and has an integral silencer in the barrel assembly. Oddly, unlike all other suppressed versions of weapons in game, the Six 12-SD features the exact same stats as the Six 12 unsuppressed, making the unsuppressed version pointless. The Six 12-SD is also unique because it is the only shotgun for the Stealth class and similarly the only suppressed shotgun.

Like the Six 12, the Six 12-SD cannot use the Ejection Port Reload.