the "antipersonnel (canister) cartridge m590 (xm590e1)" or m590 cartridge is a flechette round designed for close-in defense against massed infantry attacks. the cartridge consists of an aluminum cartridge case crimped to an aluminum canister. the canister consists of a thin-walled, deep-drawn, aluminum body that contains a payload of 2,400 eight-grain (0.5 g), low-drag, fin-stabilized, steel-wire flechettes. when the canister leaves the muzzle, the pressure ruptures the canister along inscribed score marks to release the flechettes, which disperse in a cone angle of approximately 8 degrees.