Callahan's Magnum

 is a weapon which was added to Fallout 3 with the Broken Steel downloadable content pack.

Characteristics

 * Callahan's Magnum is a unique Scoped .44 Magnum that surpasses the Blackhawk ( which is the other unique Scoped .44 Magnum) in damage, damage per second and AP Cost.
 * Depending on equipment and perks, the weapon can fire 1-2 more shots in V.A.T.S. than the Blackhawk.

Location
-The magnum is found in a safe within the ruins of the Citadel if you choose to destroy it while onboard the Enclave mobile base during the Who Dares Wins quest. If the Citadel is destroyed enter the remnants and in a hidden enclosed office is the Magnum.

- To be exact the magnum can be found like this: Enter the Citadel, jump into the very large crater, find the only door in the crater, enter walk up the stairs, it is in a safe that is next to one of the office cubicles, the safe is called Callanhan's Safe.

NOTE: This is the only upside to destroying the Citadel, but be warned the weapon degrades quickly, and now ALL Brotherhood of Steel members will attack you on sight.

Trivia

 * The weapon's name is a reference to Harry Callahan from the Dirty Harry movies who carries a .44 Magnum as his signature weapon, even though in the films it was never scoped.