Like the standard scoped .44 magnum, Blackhawk is a powerful, accurate sidearm. It deals more damage than a sniper rifle, and holds a single bullet more. It has no recoil when looking down the scope and firing.
Callahan's magnumBroken Steel - Named after famous gunfighter and security guard Harold Callahan, Callahan's magnum is the more effective version of Blackhawk, dealing more damage with less wear and tear.
Paulson's revolverMothership Zeta (add-on) - Drawn by space cowboy Paulson in the hostile confines of Mothership Zeta, it lacks the scope and fires a slew of pellets instead of a single bullet.
Upon completion of Agatha's Song, you can bring Agatha a sheet music book. She will offer Blackhawk as a reward. To get the weapon in full condition when you receive it, be polite to Agatha when both accepting the quest and receiving the pistol after completing the quest. You must use the reward speech option to get Blackhawk. Picking "sure, anything that you can afford" will get you the weapon without a Karma change; picking "No, no, a reward won't be necessary" will give you positive Karma but no Blackhawk.