The scoped .44 magnum is a very high-powered pistol, doing 10 more points of damage than the .32 hunting rifle. It has a very long effective range, which is further extended by the scope, but also has a low rate of fire for a double-action revolver. It's significantly lighter than a sniper rifle and carries a single round more in capacity.
When looking through the scope and firing, there will be no recoil, allowing the player to snipe multiple targets more easily than with an actual sniper rifle, but causing less damage. The firing rate is also higher than the .308 rifle, so this may make up for the lower power when used for sniping.
Blackhawk - While it is much stronger than the regular .44, it is also the weakest of the unique versions. However, it is the most powerful version in the original game with no add-ons.
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 slightly more 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.
Wernher's scoped .44 magnumThe Pitt (add-on) - An unobtainable version of the scoped .44 magnum carried by Wernher. It has significantly higher health but is otherwise identical to the standard variant.
Broken Steel In the Presidential metro, at the top of a set of stairs covered in rubble, the magnum is at the top of one of these flights. It is advised to have the Pip-Boy light on, or ask Dogmeat to sniff it out, as the weapon blends in quite easily with the rubble and can be hard to spot.