Full Metal Jacket
Also: FMJ
A bullet whose soft lead core is fully wrapped in a harder metal jacket, leaving only the base exposed. Built to hold together and resist deformation.
A full metal jacket bullet encloses its lead core in a copper-alloy shell across the nose and sides, with the base left open from the forming process. The jacket lets the bullet take rifling and high velocity without shedding lead in the bore, and it keeps the nose intact on impact rather than expanding.
FMJ is the workhorse of plinking and military ball ammunition because it feeds reliably and costs less than bonded or match designs. It is not a target bullet: the jacket concentricity and meplat uniformity that drive a high ballistic coefficient are held to looser standards than on an open-tip match projectile.