I learned this today. A gun silencer works by reducing the speed of the gases that push the bullet out of the barrel, but it cannot silence the sound of the sonic boom from the bullet.
A gun fires a bullet that comes from a cartridge. The cartridge that you load into a gun has three parts. The primer at the bottom. This is the fuse and contains a small explosive charge. When you fire the gun, the firing pin hits the primer, igniting the explosive. The next part of the cartridge is the propellant. This is a chemical explosive, usually a nitrocellulose-based mixture, that “propels” the bullet out of the barrel. The primer ignites and ignites the propellant which becomes a gas. The gas fills the finite space of the barrel until it reaches maximum pressure and pushes the bullet out. It takes about 1.5 milliseconds from pulling the trigger to the bullet leaving the gun. The last part of the cartridge is the bullet.
When a gun is fired, sound comes from two things: the muzzle blast and the sonic boom of the bullet. The muzzle blast is caused by the high-pressure gases escaping and expanding from the muzzle of the gun, after the bullet has left the barrel. The sonic boom is caused by the bullet travelling faster than the speed of sound. The average bullet travels at about 1000 meters per second. The speed of sound is 343 m/s. When the bullet travels faster than the speed of sound, it creates a shockwave, which is the sonic boom we hear from the bullet.
A gun silencer can cut down on the sound of the muzzle blast by giving the gases somewhere to expand, but it can’t do anything about the sonic boom from the bullet because that happens after the bullet has left the gun.
A silencer that attaches to the end of the gun has expansion chambers and baffles. The expansion chamber is a space to give the expanding gases a chance to expand and slow down before they leave the gun. The silencer then has more chambers and baffles towards the end of it. Once the expansion chamber has slowed the gas down a little, the extra chambers slow it down even more. The baffles are curved pieces of metal that have a hole in the middle to let the bullet pass. They are curved back towards the gun barrel so they deflect the gas backwards and slow it down even more. When the gas finally leaves the barrel it has lost most of its speed, cooled down, and is much quieter.
The silencer also reduces muzzle flash because that is caused when the unburned gases burn on contact with the air. When you use a silencer, the unburned gases burn in the silencer.
The silencer was invented in 1902, by Hiram Percy Maxim. They dampen down the sound of a gun, but they are nowhere near as quiet as they are in the movies. However, in 2020, the United States Marine Corps has started to issue sound suppressors to its troops. The suppressors reduce the sound of the guns enough that the soldiers can communicate more easily during a firefight. Now, that is smart.
So, a silencer makes a gun quieter by giving the high-pressure gases that push the bullet out of the barrel somewhere to slow down and cool down before they leave the barrel. However, they cannot reduce the sound of the bullet’s shock wave. And that is what I learned today.
Sources
https://en.wikipedia.org/wiki/Silencer_(firearms)
https://en.wikipedia.org/wiki/Sound_baffle
https://www.popularmechanics.com/adventure/outdoor-gear/a28357/suppressor-clear-slow-motion/
https://www.explainthatstuff.com/bullets.html
https://en.wikipedia.org/wiki/Lock_time
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