.44 Magnum revolver (Fallout 2)

The .44 Magnum Revolver is an iconic handgun used by Clint Eastwood in the Dirty Harry movies. It appears as a a small gun in Fallout 2 and Fallout 3. In Fallout 2, can be upgraded to the .44 Magnum (Speed Load). This weapon returns in Fallout 3, along with a scoped version.

In-game description
Being that this is the most powerful handgun in the world, and can blow your head clean-off, you've got to ask yourself one question. Do you feel lucky? Well, do ya punk?

Location
Flick in the Den sells this weapon, as does Happy Harry in Vault City.

Fallout 3
The .44 Magnum Revolver returns in Fallout 3 as the Scoped .44 Magnum.

The normal .44 Magnum is only obtainable through console commands, and it is used by the Mysterious Stranger.

It's also available at Flaks store at Rivet City. Also a number of ghouls in the underworld have it.