The silenced .22 SMG is a distinctive weapon with its unusual pan magazine, which sits atop the gun rather than under. The silencer is integrated into the barrel with no modification required.
However, it shares the common weakness of most shotguns and automatic weapons in Fallout: New Vegas, in that much of its theoretical power is negated by the damage threshold system. In addition to losing much of its damage, the high spread of this weapon requires the player character to be at close ranges for all of the rounds fired to impact on the target.
The Tops - when you first confront Benny in the Casino in the New Vegas Strip, his guards will be carrying them. Chairman Greeter will usually have this weapon, and can be easily killed (when Hidden) as he walks past the stairs to The Aces
With the expanded drums mod, the iron sights also appear to be modified slightly, as they would need to be raised to accommodate the larger pan magazine.
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