Subsonic ammunition is

ammunition Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other we ...

designed to operate at velocities below the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as we ...

, which at standard conditions is or Mach 1. This avoids the supersonic shockwave or "crack" of a supersonic bullet, which, particularly for suppressed firearms, influences the loudness of the shot. 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. __TOC__

Standard calibers

Subsonic versions of standard rounds

In this instance, heavier bullets are loaded in standard ammunition, which reduces muzzle velocity below the speed of sound. As an example, the very common

9×19mm Parabellum The 9×19mm Parabellum (also known as 9mm Parabellum or 9mm Luger or simply 9mm) is a rimless, tapered firearms cartridge. Originally designed by Austrian firearm designer Georg Luger in 1901, it is widely considered the most popular handgun ...

standard military round is a bullet at velocities typically around . Subsonic loads for 9mm commonly use bullets at velocities of . For these ammunition loads, balancing bullet weight and velocity are required to ensure that the ammunition will still reliably cycle semi-automatic firearms. Subsonic ammunition with normal bullet weights often fails to properly function in such firearms.

Inherently subsonic calibers

Some ammunition types were inherently designed with heavier, slower standard bullet weights and velocities. For example, the traditional American military standard

.45 ACP The .45 ACP ( Automatic Colt Pistol) or .45 Auto (11.43×23mm) is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, for use in his prototype Colt semi-automatic pistol. After successful military trials, it ...

ammunition load, of a 230

grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

bullet at 850

feet per second The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). The correspond ...

, is naturally subsonic.

Specialized subsonic calibers

Alternatively, specialized firearms and ammunition may be used to optimize total subsonic ammunition effectiveness. These are designed from the start as dedicated subsonic projectile systems. Some examples include

.300 Whisper The .300 Whisper is a CIP standard cartridge in the Whisper family, a group of cartridges developed in the early 1990s by J.D. Jones of SSK Industries. It was developed as a multi-purpose cartridge, capable of utilizing relatively lightweight ...

/ 300 AAC Blackout (7.62×35mm), .338 Whisper,

9×39mm The 9×39mm is a Soviet rifle cartridge. History and design The 9x39 is based on the Soviet 7.62×39mm round, but with the neck expanded to fit a 9.3 mm bullet. Final design was completed by N. Zabelin, L. Dvoryaninova and Y. Frolov of the Ts ...

, 12.7×55mm STs-130,

.510 Whisper The .510 Whisper is a subsonic rifle cartridge developed by SSK Industries for use in suppressed rifles. It is capable of firing a .51-caliber bullet weighing at roughly . Overview The .510 Whisper (13×47 mm) is the second of two 1/2 inch ca ...

Use with suppressors

William J. Murphy, Gregory A. Flamme, Adam R. Campbell, Edward L. Zechmann, Stephen M. Tasko, James E. Lankford, Deanna K. Meinke, Donald S. Finan & Michael Stewart (2018) The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition, International Journal of Audiology, 57:sup1, S28-S41, DOI: 10.1080/14992027.2017.1407459 Combined with firearm sound suppressors, subsonic ammunition may significantly reduce sound levels compared to normal ammunition. Specific reductions depend on the ammunition and suppressor. The peak sound pressure levels of a Remington 700 .223 caliber bolt-action rifle firing high-velocity (supersonic) ammunition using a GEMTECH G5-5.56 suppressor. The peak sound pressure levels of a Remington 700 .223 caliber bolt-action rifle firing low-velocity (subsonic) ammunition using a GEMTECH G5-5.56 suppressor. Compared to the high-velocity (supersonic) unsuppressed condition, the combination of subsonic low-velocity ammunition and a firearm suppressor provided a reductions of 45, 38, 40, and 48 dB, peak sound pressure level at the muzzle, left, right ears and behind the shooter, respectively.

References

{{reflist Ammunition