.577 may refer to:
- .577 Nitro Express, a rimmed cartridge in the Nitro Express series of big-game hunting ammunition
- .577 Snider, a British black powder metallic cartridge
- .577 Tyrannosaur, a type of cartridge developed by A-Square in 1993 for big game hunting in Africa
- .577/450 Martini-Henry, a black powder, centerfire round used by the British and British Empire militaries
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