The .577/.500 Magnum Nitro Express is a British centerfire fire rifle cartridge. Designed as a black powder round in the mid-1880s, it was based on the .577 Nitro Express, necked down to .500" (12.7mm), and was later offered in a smokeless version. While it resembles the .500 No. 2 Express, they are not the same. Moderately popular in its day, the round has long since ceased to be offered commercially. Black powder rifles in this caliber should not use heavy smokeless loads.