Ammunition designed to operate at velocities below the speed of sound
.22 Long Rifle Remington Subsonic hollowpoint ammunition
Subsonic ammunitions are ammunitions designed to operate at velocities below the speed of sound (Mach1), 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.
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.
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.
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]
^Paulson, Alan C (1996). Silencer History and Performance, Vol 1: Sporting And Tactical Silencers. Paladin Press. ISBN0-87364-909-5.
^Paulson, Alan C; Kokalis, Peter G.; Parker, N.R. (2002). Silencer History and Performance, Vol 2: CQB, Assault Rifle, and Sniper Technology. Paladin Press. ISBN1-58160-323-1.
