Subsonic ammunition

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 standard military round is a 7.5 g bullet at velocities typically around 360 m/s. Subsonic loads for 9×19mm Parabellum commonly use 9.5 g bullets at velocities of 300 m/s.

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 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 14.9 g bullet at 259 m/s, 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

Main article: Suppressor#Subsonic ammunition and reduced sonic signature

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

References

1. Paulson, Alan C. (1996). "Silencer History and Performance, Vol 1: Sporting And Tactical Silencers". Paladin Press.
2. Paulson, Alan C. (2002). "Silencer History and Performance, Vol 2: CQB, Assault Rifle, and Sniper Technology". Paladin Press.
3. Shooting Range Industries. Shooting Terms; What Is Bullet Drag, Bow Shockwave, Mach Speed Number, Boat Tail & More - Shooting Range Industries. [online] Available at: http://www.shootingrangeindustries.com/shooting-terms-what-is-bullet-drag-bow-shockwave-mach-speed-number-boat-tail-more/
4. Murphy, William J.. (2018-01-26). "The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition". International Journal of Audiology.