Finding the culprit
Knight Torres, the quartermaster for the Brotherhood of Steel in the Hidden Valley bunker, will mention that she is missing one laser pistol from her inventory, which you can volunteer to help find. After speaking to the Knight Torres, head over to the range and speak to the Paladin sitting at the desk at the firing range. Mention the pistol, and he will mention that Initiate Stanton has it. It is necessary to do this before talking to Initiate Stanton, or else Stanton will claim he doesn't know anything about it.
Speak to Stanton (at night he can be found in the initiate barracks in the first bunker area, opposite the long oval-shaped hallway from the firing range; during daytime he may be found in the classroom) and mention that he took a pistol out. He will talk about how he and Watkins went out to Scorpion Gulch for a "training exercise." Once he and Watkins realized the scorpions were more than they could handle, they ran away and he dropped the pistol in the confusion. If you mention the pistol being checked back in, he tells you that he falsified the records. Volunteer to retrieve the pistol.
Finding the pistol
Head outside and go to the Scorpion Gulch. If you turn to southeast once you leave the bunker, you should see a section of fence broken down and that leads to Scorpion Gulch. If you fast-travel, the game may deposit you in the air above the gulch (causing minor fall damage) and second of all, there will be a bunch of scorpions to deal with, fast-traveling will put you right in the middle of them (unless the area was recently cleared out). Approaching the gulch on foot doesn't take that long, and you should come across a rock with a dead prospector leaning against it. Go east-southeast from here into a small valley. Pick up the missing laser pistol sitting on top of the rock in the center (be aware that picking it up causes six or more bark scorpion hunters and a giant radscorpion to appear even if you have cleared out the area) and return it to the quartermaster for a reward.
Getting the reward
After the turning the laser pistol in, the quartermaster will have repaired a broken tri-beam laser rifle and reward the player with it. The player will also receive some fame with the Brotherhood of Steel, in addition to an initiate notifying you that the Brotherhood will leave varying amounts of energy weapons ammunition in a footlocker every couple of days for you to take, if you need it.
- Fast travel to Scorpion Gulch, it will take you right next to the rock with the pistol. Just watch out for the scorpions if you choose to do so.
- The Search and Mark perk does not highlight the missing laser pistol.
Behind the scenes
- The name of this quest could be a reference to the 1943 song "Pistol Packin' Mama". It was written and originally performed by Al Dexter but was most famously performed by Bing Crosby and The Andrews Sisters.
After speaking with Torres to begin the quest, if you ask Initiate Stanton where the laser pistol is before speaking with the paladin, Stanton only gives you the option to speak to him once, and the paladin can't be found to correct the quest.
- Possible solution: Talk to Initiate Stanton and go through all the dialogue options, then make your way to the shooting range. Talk to Knight Torres, if the dialogue does not show up to turn in the missing laser pistol. Save your game, then try talking to her again, with luck this will hopefully work and you will be able to turn in the missing laser pistol. (Also, leaving L1 to the main entrance of Hidden Valley Bunker and re-entering corrected the absent quartermaster)
- The "dead" wastelander could potentially be alive and fighting the scorpions that occupy the gulch with an invisible varmint rifle. If he dies you may loot it and all the rest of the things he has.
- A corpse may not actually be present to mark the rock: if not, it's the large one at the bottom of the "bowl".
- The tri-beam laser rifle received as a reward is bugged as it cannot place it in the same inventory with another tri-beam laser rifle; it will be replaced by the one received from Torres.
- Quest name from Fallout: New Vegas Official Game Guide