A full metal jacket (or FMJ) is a bullet encase in a copper alloy such as gilding metal, or cupronickel, or a steel alloy shell. This shell can extend around all of the bullet or often just the front and sides with the rear left as exposed lead. The jacket allows for higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore. It also prevents damage to bores from steel or armor piercing core materials. This bullet type distinguishes itself from hollow point bullets.