Subsonic ammunition is

ammunition Ammunition, also known as ammo, is the material fired, scattered, dropped, or detonated from any weapon or weapon system. The term includes both expendable weapons (e.g., bombs, missiles, grenades, land mines), and the component parts of oth ...

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 elasticity (solid mechanics), elastic medium. More simply, the speed of sound is how fast vibrations travel. At , the speed of sound in a ...

(

Mach The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a Boundary (thermodynamic), boundary to the local speed of sound. It is named after the Austrian physi ...

1), which at standard conditions is . This avoids the supersonic shockwave or "crack" of a supersonic bullet, which, particularly for suppressed firearms, influences the loudness of the shot.Shooting Range Industries. Shooting Terms; What Is Bullet Drag, Bow Shockwave, Mach Speed Number, Boat Tail & More - Shooting Range Industries. nlineAvailable at: Subsonic ammunition usually uses heavier bullets to retain as much kinetic 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 Luger, 9mm NATO or simply 9mm) is a Rim (firearms)#Rimless, rimless, Centerfire ammunition, centerfire, tapered cartridge (firearms), firearms cartridge. Originally designed by Austrian firearm designer ...

standard military round is a bullet at velocities typically around . Subsonic loads for 9×19mm Parabellum 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 firearm A semi-automatic firearm, also called a self-loading or autoloading firearm ( fully automatic and selective fire firearms are also variations on self-loading firearms), is a repeating firearm whose action mechanism automatically loads a follo ...

s. Subsonic ammunition with normal bullet weights often fails to function properly 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 ammunition load of a bullet at , 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, 300 AAC Blackout, .338 Whisper, 8.6mm Blackout, 9×39mm, 12.7×55mm STs-130, .500 Whisper, and .510 Whisper.

Use with suppressors

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 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