Subsonic ammunition

Subsonic ammunition is ammunition designed to operate at speeds less than the speed of sound, which avoids the bullet making a supersonic shockwave or "crack" as it travels. For suppressed or silenced firearms, this supersonic bullet sound would significantly add to total sound.[1][2]

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

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 115 grain (7.5 gram) bullet at velocities typically around 1,300 ft/sec (400 m/s). Subsonic loads for 9mm commonly use 147 grain (9.5 gram) bullets at velocities of 990 ft/sec (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 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 military standard .45 ACP ammunition load, of a 230 grain bullet, was subsonic.

Specialized subsonic calibers

Alternately, 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 (7.62×35mm), .338 Whisper, 9×39mm, 12.7×55mm STs-130, .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.

References

  1. ↑ Paulson, Alan C (1996). Silencer History and Performance, Vol 1: Sporting And Tactical Silencers. Paladin Press. ISBN 0-87364-909-5.
  2. ↑ Paulson, Alan C; Kokalis, Peter G.; Parker, N.R. (2002). Silencer History and Performance, Vol 2: CQB, Assault Rifle, and Sniper Technology. Paladin Press. ISBN 1-58160-323-1.