The 10mm submachine gun (SMG) is a one handed automatic weapon. Although the in-game description for the 10mm SMG lists a high damage-per-second (DPS), 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.
Another downfall of the SMG is its ammunition consumption, as this SMG can eat through 10mm rounds at alarming speeds: emptying its magazine in 3 1/3 seconds. However, with full automatic fire and a 30-round magazine, the SMG is a decent side arm for close quarters combat.
Sleepytyme - added in the add-on Gun Runners' Arsenal. It has a suppressor/compensator along with internal modifications that boost the damage and slightly elevate the rate of fire. It also comes with a darker finish and a larger magazine.