Stands for Full Metal Jacket. A bullet that is jacketed with a metal coating, often copper.

Stands for Full Metal Jacketed. A bullet completely enclosed (except for the base) in a hard metal jacket (usually an alloy of copper, sometimes a mild steel). This is the only type of bullet permitted in warfare.

Full Metal Jacket. Designation for a bullet which has a metal jacket (usually copper gilding, but sometimes steel, brass, or aluminum) surrounding the core (usually lead, but sometimes steel, tungsen, aluminum, or plastic). The bullet is designed to remain intact without deformation or expansion when striking a target. Most FMJ bullets actually have a base with exposed lead, but this is not visible when the bullet is seated in a cartridge case (see TMJ). The solid nose of an FMJ enhances feed reliability. FMJ ammunition is used by the military and is popular among private citizens for practice and plinking.