The .577 Nitro Express is a cartridge in the Nitro Express series of ammunition. The .577 is most notable for its use as the standard caliber of professional ivory hunters. It fired a 750 grain bullet (about 48.6 grams), and had a muzzle velocity of 1800 to 2100 feet per second (550 to 640 m/s), depending on the type and amount of powder used.