Subsonic ammunition

File:22 LR Remington Subsonic.jpg

.22 Long Rifle Remington Subsonic hollowpoint ammunition

Subsonic ammunition is ammunition designed to operate at velocities below the speed of sound (Mach 1), which at standard conditions is Template:Convert. This avoids the supersonic shockwave or "crack" of a supersonic bullet, which, particularly for suppressed firearms, influences the loudness of the shot.<ref name="Paulson1">Template:Cite book</ref><ref name="Paulson2">Template:Cite book</ref><ref>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/></ref>

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.

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 Template:Convert bullet at velocities typically around Template:Convert. Subsonic loads for 9×19mm Parabellum commonly use Template:Convert bullets at velocities of Template:Convert.

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 Template:Convert bullet at Template:Convert, 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

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Combined with firearm sound suppressors, subsonic ammunition may significantly reduce sound levels compared to normal ammunition.<ref name=":0">Template:Cite journal</ref> 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.<ref name=":0" />