Talking at some length to Sammy and Pauline Wins inside a shack near Westside will unravel the story that the duo looted the Vikki and Vance Casino back in Primm. They will confess to the Courier of their ambitious plan to rob one or maybe even all of the casinos on the Strip and, at this point, the Courier can either tell them that that's the worst plan they have ever heard, or pass a Speech check of 55 to assure them that their plan is great. Failing the speech challenge or bluntly replying that their plan has fatal flaws, will lead to nothing but a cold farewell. Passing the speech challenge will cause Pauline to have second thoughts about their plan and Sammy will eventually reveal the combination to open the safe containing Vance's 9mm submachine gun.
Alternatively, the player character can simply gun them down for some unique hats, but will however have to break into the safe with a lockpick skill of 100.
Behind the scenes
The code to the safe Sammy Wins gives the player character, 05-23-34, is a reference to the date the real Bonnie and Clyde were shot in Louisiana.
Talking to Sammy directly before talking to Primm Slim may cause Primm Slim to lose dialogue options relating to the quest. [verified]