The standard SIG-Sauer 14mm pistol, a large handgun with an ammunition capacity of 6 rounds likely designed for long-range pistol hunting or target shooting. It was imported to the United States from the European Commonwealth before the Great War. They were decently common early on in the survivor era, but the number of working units has swiftly declined since 2241.
In Fallout, the Sig-Sauer is a powerful, large-caliber handgun equalling the double-barreled Shotgun in damage per shot, but with a significantly greater range and magazine capacity. As such, it compares favorably to most other non-energy pistols in the game. It uses the submachine gun sprite, which makes it usable by SMG-oriented NPCs like Ian and Katja.
In Fallout 2, the 14mm pistol is crippled by the absence of hollow point ammunition -- as the only round available for the weapon, the 14mm AP (along with most other AP ammunition) was given the unfavorable Damage Modifier of 1/2. This halves the weapon's damage output, seriously affecting its usefulness in the later stages of the game.