FMJ

FMJ stands for Full Metal Jacket. In firearms terminology, it designates a type of cartridge bullet in which a soft lead core is encased by a harder metal jacket, typically copper or a copper alloy. The jacket helps prevent deformation, reduces bore fouling, and improves feeding reliability in autoloading firearms. FMJ ammunition has been widely adopted in military, police, and civilian markets, and is produced in many calibers.

FMJ bullets are generally designed for penetration and reliable performance rather than expansion. They tend not to deform or mushroom as hollow-point bullets do, which can limit stopping power in some situations and raise the risk of over-penetration in settings such as urban environments. Variants differ in jacket thickness, core material, and overall mass, and training rounds may be manufactured specifically for practice with minimal or no recoil.

Full Metal Jacket is also the title of a 1987 war film directed by Stanley Kubrick. Based on the novel The Short-Timers by Gustav Hasford, the film chronicles U.S. Marine recruits through boot camp and their experiences in the Vietnam War. It stars Matthew Modine and R. Lee Ermey, whose drill-sergeant performance is widely cited. Upon release, the film drew critical praise for performances, direction, and craft, and it has remained a notable work in the war-film genre.

Among common references, FMJ most often denotes either the ammunition style or the Kubrick film; the acronym may appear in other specialized contexts, but those two senses are the dominant ones in general reference materials.