The 9mm is the starting pistol in Killing Floor, and it is modeled after the Italian Beretta 92FS handgun.
The 9mm comes free of charge when the player spawns. The weapon can not be sold, but a second 9mm can be purchased for 150£.
The 9mm is not very powerful, and unless on a low difficulty, it is somewhat ineffective. However, the 9mm does sport decent accuracy, and can be put to good use if extra care is taken to aim for the head.