Designed to be compact yet give decent stopping power with its large .38 caliber round, this revolver is the standard issue weapon of police officers throughout Empire Bay. It's also widely used by civilians and gangsters alike.
The weapon holds 6 rounds and the player can carry an additional 6 reloading clips, for a total of 42 rounds. While giving decent performance at close range, it comes in as the least powerful weapon in the game. It occupies a slot in the right of the weapons HUD along with other one handed weapons.
They become available for sale at McClusky & Son shops in the beginning of Chapter 2. They're the default weapon of the Empire Bay Police Department throughout the game and can be easily obtained from them as well.
In all three Mafia II DLCs they're available for purchase at McClusky & Son stores from the beginning.
You can find more real world information about revolvers on Wikipedia.