There's a common idea among people who get their gun education from movies and video games that all you need to make a firearm completely silent (or at least barely as loud as someone whispering, " pew") is to attach a silencer to the front of it. For the record, they are sometimes called "silencers," but they are still far from silent. The more accurate term is "suppressors."
A suppressor works by dampening the gas that leaves the barrel after each shot. Inside the tube of the suppressor are rings, called baffles, that slow down the gas. When a round is fired normally, the gas leaves the barrel super hot and concentrated — creating a loud
and beautiful bang sound. When fired out of a suppressed firearm, the gas is slowed by the baffles and leaves cooler and dispersed — creating a less-loud phut sound.
As for the pew that comes out of every gun in Hollywood spy movies, that is entirely a work of fiction. In a May 2011 episode of MythBusters, Jaime and Adam experimented with the effects of a suppressor on an un-suppressed .45 caliber and a 9mm handgun. They had a sound engineer record the decibels and fired three shots from each gun. They repeated the experiment using suppressors and compared the results to what we see in most films.
They found that the average level of the un-suppressed handguns was 161 dB, while the suppressed firearms came in at 128 dB. Decibels are a logarithmic loudness measurement, which means that 33dB difference is very significant. An ordinary conversation at 3ft registers at about 60 dB and is the baseline for relative loudness. Although significantly quieter, 128 dB is still roughly 115.2 times louder than that baseline conversation.
Turning the math into a real-world perspective, if someone were to say the word "bang" at a normal speaking voice from three feet away under nominal conditions, a suppressed handgun would be roughly just as loud firing from 34 feet away (or roughly the width of an average 4-lane street). An un-suppressed handgun reaches that same volume at 50.5 feet away. Both still above the 125 dB threshold of pain.
And it's still not that "pew" sound.
(U.S. Marine Corps photo by Lance Cpl. Sarah N. Petrock)
One of the benefits of having a suppressor on a firearm — a benefit many who use one can attest to — is that it brings noise below the 140 dB permanent damage mark. Along with the more control of sound in the battlefield, the Marine Corps has been eyeing adding suppressors on all of their rifles and an integrated suppressor on the new M27 infantry automatic rifle. Another benefit, especially on a handgun, is that the additional weight of a suppressor at a firearm's business end helps with recoil control.
All of these are spectacular for troops, veterans, and civilian firearm owners. It just won't ever make the whispered " pew" of a Hollywood suppressor.