A suppressor is typically constructed of a metal cylinder with internal mechanisms to reduce the sound of firing by slowing the escaping propellant gas and sometimes by reducing the velocity of the bullet.
In most countries, suppressors are regulated by firearm legislation to varying degrees. While some have allowed for sporting use of suppressors (especially to mitigate the costs of hearing loss and noise pollution), other governments have opted to simply ban them from civilian use.
Suppressors disguised as microphones were used by the mercenaries in White House Down.
The suppressor is typically a hollow metal tube manufactured from steel, aluminium, or titanium and contains expansion chambers. This device, typically cylindrical in shape, attaches to the muzzle of a pistol, submachine gun or rifle. These "can"-type suppressors (so-called as they often resemble a beverage can), may be detached by the user and attached to a different firearm. Another type is the "integral" suppressor, which typically consists of an expansion or chambers surrounding the barrel. The barrel has openings or "ports" which bleed off gases into the chambers. This type of suppressor is part of the firearm (thus the term "integral"), and maintenance of the suppressor requires that the firearm be at least partially disassembled.
Both types of suppressors reduce noise by allowing the rapidly expanding gases from the firing of the cartridge to be decelerated and cooled through a series of hollow chambers. The trapped gas exits the suppressor over a longer period of time and at a greatly reduced velocity, producing less noise signature. The chambers are divided by either baffles or wipes. There are typically at least four and up to perhaps fifteen chambers in a suppressor, depending on the intended use and design details. Often, a single, larger expansion chamber is located at the muzzle end of a can-type suppressor, which allows the propellant gas to expand considerably and slow down before it encounters the baffles or wipes. This larger chamber may be "reflexed" toward the rear of the barrel to minimize the overall length of the combined firearm and suppressor, especially with longer weapons such as rifles.
Suppressors vary greatly in size and efficiency. One disposable type developed in the 1980s by the U.S. Navy for 9 mm pistols was 150 mm (5.9 in) long and 45 mm (1.8 in) in outside diameter, and was designed for six shots with standard ammunition or up to thirty shots with subsonic (slower than the speed of sound) ammunition. In contrast, one suppressor designed for rifles firing the powerful .50 caliber cartridge is 509 mm (20.0 in) long and 76 mm (3.0 in) in diameter.
Two ancillary advantages to the suppressor are recoil reduction and flash suppression. Muzzle flash is reduced by both being contained in the suppressor and through the arresting of unburned powder that would normally burn in the air, adding to the flash. Recoil reduction results from the slowing of propellant gasses, which can contribute 30–50% of recoil velocity. The weight of suppressor and the location of that additional weight at the muzzle reduce recoil through basic mass as well as muzzle flip due to the location of this mass.
When a firearm is discharged, there are three ways sound is produced. Part of it can be managed; however, some of it is beyond the ability of the operator or manufacturers to eliminate. In order of importance, the three ways a firearm generates sound are:
- Muzzle blast (high temperature, high pressure gases escaping after bullet)
- Sonic boom (sound associated with shock waves created by an object exceeding the speed of sound)
- Mechanical noise (moving parts of the firearm)
- A suppressor can only affect the noise generated by the two primary sources—muzzle blast and sonic boom—and in most cases only the former. While subsonic ammunition can negate the sonic boom, mechanical noise can be mitigated but is nearly impossible to eliminate. For these reasons, it is difficult to completely silence any firearm, or achieve an acceptable level of noise suppression in revolvers that function under standard operating principles. Some revolvers have technical features that enable suppression and include the Russian Nagant M1895 and OTs-38 revolvers, and the S&W QSPR.
Muzzle blast generated by discharge is directly proportional to the amount of propellent contained within the cartridge. Therefore, the greater the case capacity the larger muzzle blast and consequently a more efficient or larger system is required. A gunshot (the combination of the sonic boom, the vacuum release, and hot gases) will almost always be louder than the sound of the action cycling of an auto-loading firearm. Alan C. Paulson, a renowned firearms specialist, claimed to have encountered an integrally suppressed .22 LR that had such a quiet report, although this is somewhat uncommon. Properly evaluating the sound generated by a firearm can only be done using a decibel meter in conjunction with a frequency spectrum analyser during live tests.