Sunday, May 29, 2011

Suppressors a.k.a Silencers - Part I

A suppressor (or a "silencer") is a device that is screwed on to the barrel of a gun and designed to reduce the amount of noise and flash generated by a weapon. Before we start to study about these devices, it is good to clear up a few myths about them (and these myths are mainly due to Hollywood movies). The biggest myth is that they make a firearm almost noiseless -- you only hear a soft "phut" noise, if all the James Bond movies are to be believed. The second biggest myth is that in the absence of a suppressor, you can improvise with almost any cylindrical object (bottle filled with water, coke can etc.)

The first thing to note is that there are multiple sources of noise possible from a firearm:
  1. Noise of the hammer striking the cartridge.
  2. Noise due to the exploding propellant material and hot gases leaving the barrel.
  3. Noise due to the bullet flying through the air (sonic boom, if the bullet is flying supersonic).
  4. Noise due to ejecting the empty cartridge case and cocking the weapon.
  5. Noise due to bullet striking the target.
Of all these sources, #2 and #3 are the main sources of loud noise from a firearm. Let us consider the noise from #2 (i.e. exploding propellant material). This typically hits about 140-160 dB, which is louder than your average heavy metal concert (trust me on this one, I've attended quite a few of them). No suppressor is going to remove such a loud noise like this completely. At the most, a suppressor drops the sound level to around 130-145 dB, with the quietest ones measuring about 117 dB, which is still in heavy metal concert territory. So, what's the use of such a device if it doesn't remove the sound completely. Well, when hearing protection is added, this makes the loudness level easier to bear. These devices also remove the flash emanating from the barrel and thus make it less likely to disorient shooters. They also change the sound signature of a firearm, so that the sound doesn't exactly sound like a shot. As the old Finnish expression goes, "A silencer does not make a marksman silent, but it makes him invisible".  You can observe how the sound signature changes in the below video, where the person fires a 9 mm. pistol, first with no suppressor and then with a suppressor screwed on:

As you may note, the suppressor doesn't completely remove all the noise, but it does remove a fair amount and also the sound no longer sounds like a gunshot.

There were many inventors of silencing devices towards the end of the 19th century, with one patent granted to J. Borrensen and S. Sigbjornsen for a device that "lessens the sound of discharge" in 1899. However, the earliest successful commercial suppressor was invented in 1908 by the American inventor, Hiram Percy Maxim, the son of Sir Hiram Stevens Maxim, the man who invented the first portable automatic machine gun. His device consists of a hollow cylindrical tube with a number of expansion chambers in it.

This device is screwed on to the end of the barrel. Expanding gases from firing the cartridge are trapped by the baffle plates, while the bullet travels through the hole in the center. The trapped gases expand and cool and thereby exit out of the barrel with less pressure and velocity, which reduces the noise. This device was sold under the trademarked name "Maxim Silencer", which is probably why we still call suppressor devices as "silencers" even though they don't actually silence a firearm completely.

Mr. Hiram P. Maxim also had interests in the emerging automobile industry and he developed a similar device to reduce engine noise, which we still use today: the muffler, which is also known as a "silencer" in some parts of Asia and Europe.

Since these devices don't entirely remove the noise, the firearms industry prefers to call them "suppressors" instead of "silencers". In our next post, we will look into more about such devices.

1 comment:

  1. Thanks for your helpful insights on the commonly misunderstood topic of firearm suppression. Your article was well-written and on point. Looking forward to the Part II post on this subject.