Vance and his wife Vikki were "master criminals" before the Great War. The player can hear the story of Vikki and Vance by consulting Primm Slim in the Vikki and Vance Casino. Slim's account implies that Vikki and Vance were in fact small-time white-collar criminals. According to Slim, Vance purchased a high-quality mint condition 9mm machine gun immediately prior to his death but never fired it.
Vance's 9mm SMG has several differences from the standard 9mm SMG. First and foremost, it does more damage, the damage-per-second is higher, and it has a drum magazine with a greater capacity. Aesthetically, it is in pristine condition with wood or Bakelite grip panels, lacks a stock, and has a different Express-type iron sight.
Its high rate of fire, common ammunition, and high DPS make it a valuable weapon to a character skilled in Guns.
The weapon is missing from its display case in the Vikki and Vance Casino, but Primm Slim does not notice this fact. With high enough Science skill (50), however, you will gain a dialog option to reveal that the weapon was taken to Wins hideout, where it can be found inside the safe with a very hard lock. The lock can be picked, or, with a high enough Speech skill (55), you can convince the Wins to give you the combination. If your Speech skill isn't high enough, talk to Sammy again and another dialog option will appear.