Hornady Subsonic Ammunition is designed for accuracy and performance below the speed of sound. The Sub-X (Subsonic – eXpanding) bullet features a lead core. Long grooves in its gilding metal jacket combine with the bullet’s flat profile and the patented Flex Tip insert within its hollow-point cavity to help it expand reliably at low velocities. Performance of the Hornady Subsonic load meets or exceeds FBI Protocol terminal ballistic test requirements.  Other features:• Loaded with unique powders optimized for subsonic use, the low flash signature is ideal for both suppressed and unsuppressed performance.• Bullets feature a cannelure for a positive case crimp for use in semi-autos.• Designed specifically to fit, feed, and function in a variety of firearms including gas system guns.