A Pair of Dead Desperados, II

 is an unmarked quest in Fallout: New Vegas.

Quick walkthrough
Talking to Sammy and Pauline Wins at their shack near Westside reveals they looted the Vikki and Vance Casino back in Primm. They will tell the Courier of their ambitious plan to rob all the casinos on the Strip, and the player can either tell them that's the worst plan they've ever heard, or pass a Speech check of 55 to tell them that the player thinks that the plan is great. Doing this will cause Sammy to give you the combination to the safe containing Vance's gun.

Alternatively, the player can simply gun them down for some unique hats.

Bugs

 * Once you have obtained the gun, Primm Slim may no longer talk with you, except to say "Always good to see you partner, anything I can help you with?", without any text dialog or options. This results in you not being able to return the gun to the casino.
 * If you kill Sammy and Pauline without starting the quest of getting Vance's gun, you won't find the gun on Sammy, Pauline or in their Very Hard Locked safe.
 * If you kill Sammy and Pauline with the quest and steal the gun, Primm Slim keeps asking if you found the gun. You cant return it.