This specific type of cartridge combines the .45 ACP case with a projectile traveling below the speed of sound (generally less than 1,125 feet per second). This results in reduced noise compared to standard supersonic ammunition, making it advantageous in certain scenarios. A common example utilizes a heavier bullet, often in the 230-grain or higher range, to achieve subsonic velocities without dramatically reducing kinetic energy.
The reduced auditory signature offers significant tactical advantages for suppressed firearms, minimizing the report and making it more difficult to locate the shooter. Furthermore, the heavier bullets typically used in this type of ammunition often exhibit improved terminal ballistic performance at subsonic velocities compared to lighter, faster projectiles. Historically, specialized units needing discretion and suppressed fire have favored such rounds. This specialized ammunition has seen increasing use in competitive shooting disciplines and hunting applications where noise reduction is beneficial.