.577/500 Magnum Nitro Express

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.

In power, the .577/.500 is comparable to the contemporary .50-110 Winchester, or the modern .30-'06. It is sufficient for elk, deer, moose, or bear at medium range or in woods and thin-skinned dangerous game, including tiger and lions, but not thick skinned ones such as the rhinoceros. It was favored more in India than Africa by contemporary shooters, and tended to be offered in heavy rifles.

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.