Full metal jacket (FMJ) ammo is a type of bullet used in small-arms that consists of a soft lead core encased in an outer shell of harder metal, such as copper, brass, cupronickel, or steel alloy). The jacket allows for higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore, and it also prevents damage to bores from hard steel or armor-piercing core materials). FMJ rounds are commonly used for target shooting at ranges or in backyards. The key feature of any FMJ bullet is that the nose and sides of the lead bullet will be completely covered by the jacket. FMJ ammunition can also be called other things like full metal case or have additional suffixes like “boat tail” to let you know the intended use of the bullet or how it will perform. FMJ bullets are often used for practice, while hollow point bullets are used for self-defense.