The .500 Bushwhacker is a .50 caliber semi-rimmed revolver cart...
wikipedia - 26 Dec 2022The .500 Bushwhacker is a .50 caliber semi-rimmed revolver cartridge developed by TII Armory for the Magnum Research BFR revolvers. It is currently the most powerful revolver cartridge in the world, offering a similar level of ballistic performance to African stopping rifles, such as the .416 Rigby and .470 Nitro Express. Given comparable barrel lengths, it is nearly twice as powerful as the .500 S&W Magnum.[4]