Subsonic ammunition

Subsonic ammunitions are ammunitions designed to operate at velocities below the speed of sound (Mach 1), which at standard conditions is 340.29 m/s (1,116.4 ft/s). This avoids the supersonic shockwave or "crack" of a supersonic bullet, which, particularly for suppressed firearms, influences the loudness of the shot.^[1][2][3]

Subsonic ammunition usually uses heavier bullets to retain as much energy as possible at the lower velocities. Some subsonic ammunition is used in non-suppressed firearms to gain the advantages of heavier bullet weights.