Pfeifer Zeliska .600 Nitro Express revolver

The .600 Nitro Express Zeliska revolver is an Austrian single-action revolver produced by Pfeifer Waffen. Except for the Giant 1859 28mm Remington revolver, the Zeliska may be the largest handgun in the world, weighing in at 6 kilograms (13.23 lb) and having a length of 55 centimetres (21.65 in).

Source: Wikipedia — Pfeifer Zeliska .600 Nitro Express revolver (CC BY-SA 4.0)