There are many benefits with silencers or suppressors on military rifles such as the M16 or M4 assault rifles. The suppressor can reduce the recoil significantly as it traps the escaping gas. This gas masses a little less than one half the projectile mass, with the gas exiting the muzzle at about twice the projectile's velocity, thus giving a reduction in the felt recoil of approximately 50%. The added weight of the suppressor also contributes to the reduction of the recoil, though a significantly heavy suppressor would unbalance a weapon.
Early silencers were created around the beginning of the 20th century by a number of inventors. American inventor Hiram Percy Maxim is credited with inventing and selling the first commercially successful models circa 1902. Maxim called his device the trademarked name Maxim Silencer.
Later this style silencer would be widely adapted to internal combustion engines to generate the muffler, still called a silencer in the UK. The term silencer has since fallen out of favor among the firearms industry, being replaced with the more accurate term sound suppressor or just suppressor. Common usage, in newsprint and in non-technical usage favors the technically inaccurate, but historically first term that was used, silencer.
The suppressor was first introduced into the United States Army Air Forces before World War II. Office of Strategic Services agents during World War II favored the newly-designed High Standard HDM .22 caliber pistol. The addition of a sound suppressor baffle to the barrel absorbed 90% of the noise. The suppressor also has the often-neglected benefit that it reduces muzzle flash by as much as 90%. This is very important as much fighting takes place at nighttime, and soldiers are commonly trained to identify and shoot at muzzle flashes in combat situations.
A military issued suppressor that is "married" correctly to the rifle has very negligible disadvantages, namely their weight and length.
Suppressors are also useful for target shooting, as the reduced noise can prevent ear damage to the user of a firearm. In the United States, it is legal in most states for an individual to possess and use a silencer / suppressor; however, one must go through the National Firearms Act process administered by the BATFE. Such transfers also require a federal tax payment of two hundred dollars and a thorough background check.
The suppressor is typically a hollow cylindrical piece of machined metal that attaches to the muzzle of the pistol or rifle. Some others are designed as an integral part of the weapon, and may include an expansion chamber that partially surrounds the barrel (These are often called "integral" designs, a reference to old-fashioned collapsing telescopes). The outer casing of the suppressor is typically referred to as the can.
The suppressor reduces noise by allowing the rapidly expanding gasses from the explosion of the round to be briefly diverted or trapped inside a series of hollow chambers. The trapped gas can expand and cool, reducing the pressure and velocity as it exits the suppressor. The divisions between these chambers are called baffles. There are typically at least 4 and up to perhaps 15 chambers in a suppressor, depending on intended use and design details. The engineering design of modern suppressors is analogous mathematically to the design of electrical filters, and many of the same design techniques may be used to design either.
Often, a single, larger expansion chamber is right at the barrel's muzzle, which allows the propellant gas to expand considerably and slow down before most of it begins to encounter the shaped baffles or wipes section of the suppressor.
Suppressors vary greatly in size and efficiency. One disposable type developed in the 1980s by the US Navy for 9 mm pistols is 5.9 x 1.77 in and is good for six shots with standard ammunition or up to thirty with low-powered, subsonic ammunition.