Hippo. The 9×23mm Largo (9mm Largo, 9mm Bergmann-Bayard, 9mm Bayard Long) centerfire pistol cartridge was developed in 1901 for the Bergmann Mars pistol. The ro Hippo The 9×23mm Largo (9mm 9mm Bergmann-Bayard Bayard Long) centerfire pistol cartridge was developed in 1901 for the Bergmann Mars ro