page_title: Silencer (firearms)
section_title: Subsonic ammunition
hierarchical_section_title: Silencer (firearms) / Characteristics / Subsonic ammunition
caption_attribution_description: Русский: ВСС Винторез и АС ВалEnglish: VSS Vintorez and AS Val
context_page_description: A silencer, also known as a sound suppressor, suppressor or sound moderator, is a muzzle device that reduces the acoustic intensity of the muzzle report and the recoil when a gun is discharged, by modulating the speed and pressure of the propellant gas from the muzzle and hence suppressing the muzzle blast. Like other muzzle devices, a silencer can be a detachable accessory mounted separately onto the muzzle, or an integral part of the barrel.
  A typical silencer is a metal cylinder containing internal sound baffles, with a hollow bore to allow the projectile to exit normally. During firing, the bullet flies through the bore with little hindrance, but most of the expanding gas ejecta behind it is retained through a longer and convoluted escape path created by the baffles, prolonging the release time. This slows down the gas and dissipating its kinetic energy into a larger surface area, reducing the blast intensity, and thus lowering the loudness.
  Silencers can also reduce the recoil during shooting, but unlike a muzzle brake or a recoil compensator, which reduce recoil by vectoring more of the blast impulse laterally, silencers release almost all the gases towards the front.
context_section_description: In weapons firing supersonic ammunition, the bullet itself produces a loud and very sharp sound as it leaves the muzzle in excess of the speed of sound and gradually reducing speed as it travels downrange. This is a small sonic boom, and is referred to in the firearm field as "ballistic crack" or "sonic signature". Subsonic ammunition eliminates this sound, but at the cost of lower velocity, resulting in decreased range and much decreased muzzle energy, thus lessening effectiveness on the target; this can be compensated for by increasing bullet weight. For example, if the muzzle velocity is reduced from 2,700 ft/s (820 m/s) (common for the .308 Winchester, for example) to a subsonic 950 ft/s (290 m/s), the muzzle energy is reduced by a factor of 8. Military marksmen and police units may use subsonic ammunition in suppressed rifles, when minimal noise is more important than range and energy.
  However, the numeric effectiveness of subsonic rounds is, again, misrepresented by media. Independent testing of commercially available firearm suppressors with commercially available subsonic rounds has found that .308 subsonic rounds decreased the volume at the muzzle by 10 to 12 dB when compared to the same caliber of suppressed supersonic ammunition. When combined with silencers, the subsonic .308 rounds metered between 121 and 137 dB.
  The ballistic crack depends on the speed of sound, which in turn depends mainly on air temperature. At sea level, an ambient temperature of 70 °F (21 °C), and under normal atmospheric conditions, the speed of sound is approximately 1,140 feet per second (350 m/s). Bullets that travel near the speed of sound are considered transonic, which means that the airflow over the surface of the bullet, which at points travels faster than the bullet itself, can break the speed of sound. Pointed bullets, which gradually displace air, can get closer to the speed of sound than round- or snub-nosed bullets before becoming transonic.
  Special cartridges have been developed for use with a silencer. These cartridges use very heavy bullets to make up for the energy lost by keeping the bullet subsonic. A good example of this is the .300 Whisper cartridge, which is formed from a necked-up .221 Remington Fireball cartridge case. The subsonic .300 Whisper fires up to a 250 grains (16 g), .30 caliber bullet at about 980 feet per second (300 m/s), generating about 533 foot-pounds force (723 J) of energy at the muzzle. While this is similar to the energy available from the .45 ACP pistol cartridge, the reduced diameter and streamlined shape of the heavy .30 caliber bullet provides far better external ballistic performance, improving range substantially.
  9×19 mm Parabellum, a very popular caliber for suppressed shooting, can use almost any factory-loaded 147 grains (9.5 g) weight round to achieve subsonic performance. These 147 gr weight bullets typically have a velocity of 900–980 feet per second (270–300 m/s), which is less than the 1,140 feet per second (350 m/s) speed of sound.
  The Soviet/Russian armor-piercing 9×39mm ammunition used in rifles such as the AS Val has a high subsonic ballistic coefficient, high retained downrange energy, high sectional density, and moderate recoil.
  Without using subsonic ammunition, the muzzle velocity of a supersonic bullet can be lowered by other means, before it leaves the barrel. Some silencer designs, referred to as "integrals", do this by allowing gas to bleed off along the length of the barrel before the projectile exits. The MP5SD is an example of this, with holes right after the chamber of the barrel used to reduce a regular 115 or 124 gr ammunition to subsonic velocities.
caption: Integral silencer on VSS Vintorez sniper rifle and AS Val assault rifle
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