How a gun silencer work?


How a gun silencer work?

In: Physics

When the powder in the casing explodes the excess gass goes into the tubes of the silencer instead of the air outside. The explosion is what creates the noise so when the excess Gass enters the silencer the noise from the explosion is minimal but not completely gone.

Sound is a pressure wave in gas, the higher the pressure and more energy it has the louder it sounds.

A silencer, more accurately a suppressor, channels the expanding gases from a fired cartridge through a series of traps that slow the gas and make it lose energy, pressure and so volume before it finally escapes.

Suppressors have a series of internal baffles that reduce the acoustic, pressure, and speed of the gas being discharged of the shot.

Imagine a kindergarten. When it’s 12 o’clock, all the little children are leaving at the exact same moment, immediately running out the door, screaming and flailing their arms as children do. If you stand right outside the door, you are deafend by the noise! This is the explosion you hear from a normal gun.

Now imagine you build right outside the door a bunch of corridors, each leading to a different area, each curved and full of corners. The children randomly split into these corridors and get super exhausted having to navigate them. By the time they exit the corridor, they each face a different direction and are tired, so they make very little noise. This is your basic noise suppressor.

There are multiple ways that a sound suppressor might work. It is common to use several of these techniques at the same time. For some guns resisting air from exiting out the barrel in front of the bullet will slow it down enough to become subsonic so you do not get the crack of breaking the sound barrier. But this does not work for most guns and also reduces the effectiveness of the guns where it does work on. So most suppressors actually help gasses to escape.

Another technique is to have baffles around the path of the bullet placed at exact distances to cause destructive resonances at the sound frequencies they try to suppress. You need several such chambers, one for each major frequency characteristic for the sound of that gun. In addition to this suppressors have chambers for the gasses to expand into filled with absorbing materials to dampen the sound.

The last technique you might see is rarely used properly and is rubber wipes. By closing off the muzzle of the gun with rubber the bullet may still be able to force its way through the rubber but then it closes up behind them and prevents the loud gasses from the explosion to exit through the same way. This only works for slow bullets and the wipes wear out very quickly so you need to replace them as you reload the magazine.

It should also be noted that none of these devices silences a gun. There is just too much noise coming from a gun to make it even close to silent. What a sound suppressor does is to reduce some of the loudest noises. It is used on some gun ranges to reduce neighbor complaints and make it possible to be in the area without ear protection.

Silencers/suppressors/mufflers/cans slow down the expansion of the gases ejected at the muzzle when a bullet exits the barrel. These gases are what was projecting the bullet.

When they suddenly are allowed to exit in nearly all directions, as well as meet fresh oxygen and relatively cold air, you hear a boom and see a fireball. When the bullet breaks the sound barrier (1060 to 1200 fps depending on the environment), there is also a crack sound.

The silencer constricts these gases into a device that is specifically made to slow them down, usually by having them run into a series of walls (baffles). The spacing and amount of these walls have different effects on the silencer’s performance. Many companies have many different takes on what works best in terms of actual decibel reduction for a specific use-case.

Because these gases are cooling down more slowly and slowing down more quickly (a few milliseconds) the sound of the gases exiting the “muzzle” of the suppressor is lower.

No silencer alone can eliminate the cracking sound of a supersonic bullet. This is why lots of silencer enthusiasts tell beginners that chasing raw decibel reduction for a caliber like the AR-15’s standard 5.56×45 is mostly futile.

Subsonic rounds do exist for traditionally supersonic calibers, which do not produce a cracking sound when breaking the sound barrier. However, if the round was not already on the border of breaking or not breaking the sound barrier, then they tend not to work well.

Thats why the Soviets never went through with making an integrally suppressed AK-74; the difference in lethality between subsonic and supersonic rounds was huge for that caliber. Which is where the 9×39 caliber was conceptualized.

There are some variants of guns which can take a supersonic round, and bleed off gasses into an integral suppressor early on, making the round subsonic upon exit.

The most famous of which is the MP5SD. But without a ported barrel, the rounds would still be supersonic; the can doesn’t change that, it just catches those gases so that there’s no explosive noise at the barrel port. Bullets fired from traditional suppressors are often marginally faster than their unsuppressed counterparts (take that, video games).

Not to mention, if F=m*a, and the mass remains constant, the slowing down of the bullet will in fact have a negative impact on the bullet’s performance, which is why lots of special secret squirrel units/agencies are ditching the MP5SD.

A gun works this way: The primer ignites the powder. The powder then burns, producing gases with increasing pressure. When pressure is enough, it dislodges the bullet from the case and starts pushing it down the barrel.

From here, we will consider the .223 Remington. The pressure in the chamber can hit about 55,000 psi, extremely high. Given the extra volume of the barrel, this pressure decreases by the time the bullet reaches the end of the barrel. But it’s still maybe 15,000 psi when the bullet leaves the barrel. There’s a lot of “it depends” in this, but we’ll go with this number.

So you have the end of the barrel, all the ambient 15 psi air around it. Then a bullet exits, and suddenly a volume of very hot 15,000 psi gas slams into the air and rapidly expands since it is no longer constrained. This makes the air have to get out of the way really fast, and boom, shockwave, same as from an explosion.

In general (depends on design), a suppressor is a tube with a bunch of small chambers in it, with dividers between those chambers that have a hole for the bullet to pass through. The gas expands to fill the first chamber, then the second, and so on before it hits the atmosphere. This extra time also allows the gases to cool more before exiting. To give you an idea of how much cooling, a suppressor can get hot enough that you may get a doctor visit level of burn if you dump a full magazine through one and then grab it (people who use them a lot often bring oven mitts or welding gloves). Shoot even more, and they can start glowing.

Due to this chance to expand and cool within the gun, the gas pressure and temperature is much lower when it hits the atmosphere, so the boom isn’t so bad. It’s still loud, just not quite as ear-splitting loud. Normally a suppressor can take about 30 dB off a gun, so we go from instant permanent hearing damage loud to needing to experience many shots to get hearing damage.

We can do more to get this quieter. Sometimes you’ll have wipes between the chambers, which are solid rubber discs the bullet has to punch through, and they mostly seal up behind the bullet, trapping the gases (they only last a few shots though). Instead of this more modern designs create turbulence to interfere with the gases leaving the barrel, kind of keeping them trapped longer by making them roll around. We can also add to the expansion volume by shrouding the whole barrel with a suppressor, allowing the gases to fill the entire area around the barrel counting as one big expansion chamber.

Suppressors do not stop the sonic boom of supersonic bullets, the “crack.” They also do not quiet the sound of the moving parts of semi-auto guns (which can be kind of loud).