Sub-X (Subsonic - eXpanding) bullets deliver big results without a big bang! Designed to provide deep penetration below the speed of sound"" Sub-X features a lead core. Long grooves in its gilding metal jacket combine with its flat profile and the patented Flex Tip insert within the bullet's hollow point cavity to help it expand reliably at low velocities. Cannelures provide positive case crimp"" making Sub-X ideal for semiautomatic weapons.