The .600 Overkill was designed by Robert Garnick of Las Vegas, Nevada, USA. The case is based on the .600 Nitro Express, with a belt [.683 in (17.35 mm)] added for headspacing and the rim to fit that of the .505 Gibbs [.640 in (16.26 mm)] size bolt face. This cartridge was intended to be the largest bullet that was able to fit in the CZ-550, and was designed specifically for the purpose of elephant hunting. The CZ-550 is able to fit 2 cartridges, with slight alterations. The .600 Overkill fires a bullet at more than ,