Looking like a shortened Barret m82A1
the Maadi Griffin is the most powerful handgun
in the world. Its low production numbers however does not qualify it as a commercially available handgun.
The Maadi Griffin is a single shot pistol or, depending on how you handle it, carbine that fires the venerable .50 BMG cartridge.
Firing one is mostly a "see, I told you I could do it." affair and is more or less a novelty. Although the compactness of its package and tremendous power of its ammo make it very suitable for mobile units that need to seek and destroy enemy vehicles, such tasks are better done from afar using a rifle.
Last time I checked the Maadi Griffin was no longer in production and the blueprints and patent is up for sale.