Dead Rising 2: Six

In Dead Rising 2 for the PS3, Xbox 360, and PC, one of the more powerful guns in the game is the Six Shooter. Obviously it will kill zombies in one shot, but more importantly, it is extremely effective against psychopaths.

The Six-Shooter is located on the saw table in the South Plaza area after you defeat the psychopath Seymour Redding in the WWJWD mission.