The Mysterious Magnum is a .44 revolver that plays the Mysterious Stranger theme when drawn or holstered. It´s owned by The Lonesome Drifter that can be found East of El Doraro Dry Lake

Once there, you will approach the Lonesome Drifter when he is sitting on the tree trunk, you will open VATS or aim at the revolver to break it

once fired, he should have dequipped his weapon and you will finish the fight by holstering your weapon

Now you will wait until he sits down again on the tree trunk, then you will go sneaking behind him, and you will pickpocket him, he will have the damaged revolver in his inventory
Then you just have to repair the weapon with another revolver or with the Jury Rigging Perk, you can just use a 9mm pistol to repair it.

Well thats it, this is basically just to tell you, if you dont know it by now, how to get the weapon without the Barter Skill to have him for the quest Talent Pool. Hope you liked my first guide and i just do this guide because i didn't see this option in other people's guide. Cya



Fun Fact: You can get two Mysterious Magnums by combining this trick *before* accepting the Tops' "Talent Pool" (or whatever the name was) quest, then just pass the Barter check . - Fact given by 5persondude