Lincoln's Repeater (Fallout 3)

Lincoln's Repeater is a .44 rifle with a 15-round magazine, found in Fallout 3. It is located, in perfect condition, inside of a display case in the top floor of the Museum of American History offices. Despite its .44 ammunition, it should be considered in the same category as the Hunting Rifle (with higher accuracy, comparable to the Sniper Rifle), as it uses its parts for repair. The rifle is devastating when used with the Commando and Sniper perks, which boost rifle accuracy in V.A.T.S. This is easily the best medium-to-long range small guns rifle in Fallout 3 as it combines accuracy, high damage, a large magazine, and low AP requirements. On Normal difficultly, sneak attack headshots (with a decent small guns skill) using this weapon will kill anything instantly bar Giant Radscorpions, Deathclaws, Super Mutant Behemoths and most robots (Robobrains and Protectron being the exceptions).

Upon entering the Museum of American History, make your way to the Lower Levels, located on the left as you enter the big room with the giant prehistoric animals. (Be aware that there are a large number of Feral Ghouls in here. Make sure you have a good weapon and possibly some health before you attempt this.) Once in there, walk up the left staircase and go into the room filled with empty (or destroyed) displays and enter the door to the offices, located near the rear left corner of the room. Make your way through the offices until you come to a large, open room with a turret on the ceiling. Walk up the staircase against a wall in the front of the room. Upon reaching the top, you should see a giant hole in the wall. Once you reach the top, however, more Ghouls are waiting for you along with a Glowing One. This guy is pretty tough if you're a low level, so make sure you have a strong weapon. Go through the giant hole, and in furthermost cubicle on the left you should find the rifle waiting inside a display case on a desk. Alternatively, you can just walk by them all without being attacked if you are wearing the Ghoul Mask.

You can also sell this to Leroy Walker, who occupies Lincoln Memorial and will destroy it to erase Lincoln's legacy. Otherwise, you can sell it to Hannibal Hamlin after receiving the Head of State quest, who will enshrine it. Alternately, you can sell it to Abraham Washington in Rivet City. Note that the price may be a lot less than its specified value (which is dependent on condition).

Trivia
This weapon is speculated to be based on the 1860 Henry Rifle, a .44 caliber black powder cartridge (known as a.44 Henry round) rimfire rifle, although it has a wooden hanguard in front, very similar to a Winchester Model 1866. Though it would seem to be plausible to use .44 magnum ammunition in the rifle with slight modifications, the pressure from the modern cartridge would be far too much for the firing chamber to handle.