The 6.5x25mm CBJ is a pistol cartridge designed for the CBJ-MS personal defense weapon during the early 2000's. It is based on the 9x19mm Parabellum, necked down to accept a 6.5mm sabot, which contains a smaller armor-piercing tungsten core projectile of .157 caliber (4mm). It is similar in overall design philosophy to cartridges such as the 5.7x28mm and 4.6x30mm.
Other firearms traditionally chambered in 9mm, such as the Brügger & Thomet MP9 have also been adapted to the 6.5x25mm cartridge. Because of the parent case being 9mm, magazines are fully compatible and the MP9 only requires a simple barrel swap in order to be converted to the new cartridge.