Fallout 3 cheat: .44 Lincoln's Repeater Rifle

Once you enter the Histroy museum to the Underworld, find a hallway on the wayto a separate section of the museum (have you guns ready for the Ghouls).

Find the office Archives or such room on the next floorand enter.

You'll be able to locatethe Repeater in a case in the historical archive room.

Be warned there is a Glowing One in the room with lots of other ghouls waiting.