Subsonic ammunition
Subsonic ammunitions are ammunitions designed to operate at velocities below the speed of sound (Mach 1), which at standard conditions is 340.29 m/s (1,116.4 ft/s). This avoids the supersonic shockwave or "crack" of a supersonic bullet, which, particularly for suppressed firearms, influences the loudness of the shot.[1][2][3]
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.
Standard calibers
[edit]Subsonic versions of standard rounds
[edit]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 grams (116 gr) bullet at velocities typically around 360 metres per second (1,200 ft/s). Subsonic loads for 9mm commonly use 9.5 grams (147 gr) bullets at velocities of 300 metres per second (980 ft/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
[edit]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 230 grain bullet at 850 feet per second, is naturally subsonic.
Specialized subsonic calibers
[edit]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 (7.62×35mm), .338 Whisper, 9×39mm, 12.7×55mm STs-130, .510 Whisper.
Use with suppressors
[edit]Combined with firearm sound suppressors, subsonic ammunition may significantly reduce sound levels compared to normal ammunition.[4] 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.
| Suppressor Condition | Muzzle (dB SPL) | Left Ear (dB SPL) | Right Ear (dB SPL) | Behind Shooter (dB SPL) |
|---|---|---|---|---|
| Unsuppressed | 176 | 160 | 160 | 148 |
| Suppressed | 148 | 134 | 136 | 120 |
| Reduction | 28 | 26 | 24 | 28 |
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.
| Suppressor Condition | Muzzle (dB SPL) | Left Ear (dB SPL) | Right Ear (dB SPL) | Behind Shooter (dB SPL) |
|---|---|---|---|---|
| Unsuppressed | 157 | 140 | 140 | 127 |
| Suppressed | 131 | 122 | 120 | 100 |
| Reduction | 26 | 18 | 20 | 27 |
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.[4]
References
[edit]- ^ Paulson, Alan C (1996). Silencer History and Performance, Vol 1: Sporting And Tactical Silencers. Paladin Press. ISBN 0-87364-909-5.
- ^ 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.
- ^ 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/>
- ^ a b Murphy, William J.; Flamme, Gregory A.; Campbell, Adam R.; Zechmann, Edward L.; Tasko, Stephen M.; Lankford, James E.; Meinke, Deanna K.; Finan, Donald S.; Stewart, Michael (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. 57 (sup1): S28–S41. doi:10.1080/14992027.2017.1407459. ISSN 1499-2027. PMC 8588962. PMID 29299940.