FMJ stands for Full Metal Jacket and describes a bullet that has a lead core completely coated with a harder metal, most often copper. This full metal jacket reduces lead residue in the barrel and helps the bullet keep its shape as it travels towards its target. JHP stands for Jacketed Hollow Point and describes a lead bullet, jacketed in a harder metal, that has a hole in its tip. This hollow point causes the projectile to mushroom upon impact, reducing the risk of over penetration and creating more stopping power.