10mm pistol

The Colt 6520 is a pistol with a revolving cylinder and is a highly durable and efficient weapon. It was developed by Colt Firearms prior to Great War, chambered in commom 10mm, proved itself resistant to desert-like conditions of the post-nuclear wasteland, a fine example of workmanship and quality (at least pre-War made exmaples, which became more scarce over time and extensive use). The construction of the gun allow it's manufacture with minimal equipment needed, allowing it to be replicated by workshops in post-nuclear world. The 6520 has no problem feeding hollowpoint ammunition for small game hunting or armor piercing rounds for larger bipedal game.

These traits (and low cost - especially of post-War exmaples) make it very popular among raiders or survivalists for whom advanced equipment requiring high maintenance would be a liability.

10mm Pistol is a Fallout and Fallout 2 weapon. In-game description: A Colt 6520 10mm autoloading pistol. Each pull of the trigger will automatically reload the firearm until the cylinder is empty. Single shot only, using the powerful 10mm round.

Behind the scenes
The 10mm pistol is a reference to the Hard Boiled comic books. Its plausibility as a real weapon is disputable, however there are real 10mm pistols available to civilians today. The 10mm Auto round is used for hunting.