How Silencers Work

How do silencers work? Physics! Who said science can’t be fun?

Before we get into the GunsAmerica 2015 Science Fair, let’s clear something up about the name. Calling a gun muffler a “silencer” is correct. Calling a gun muffler a “suppressor” is also correct. Hiram Percy Maxim, son of the guy who invented that awesome machine gun, invented the silencer way back in 1902. When he patented it in 1909, he trademarked the device as a Maxim Silencer. So the original and proper name is “silencer.” Since then, the industry has made use of the descriptive term “suppressor” since silencers don’t really silence – they suppress. It’s like those machines that bored office workers use to duplicate their butt. You can call them Xerox machines or copiers. From here on out, I’ll use the two terms interchangeably.

What maketh noise?

There are several components of gunshot noise. The big one is the sound of hot gas blasting out the muzzle. Then, with a supersonic projectile, there’s a mini sonic boom that travels down range. The noise of the action of the gun can also come into play. Silencers primarily address the big one – the sound made by rapidly expanding gas as it’s expelled from the muzzle.

The big blasty noise is a result of releasing the Kraken. In this case, the Kraken is super hot, and super compressed gas trapped in the barrel until the bullet leaves. Most bullets are one or two-thousandths of an inch larger than the bore itself, so all that Kraken gas is entirely trapped behind the bullet until the micro-second it leaves the barrel. When the hot and highly compressed gas hits the relatively cool and not at all compressed air, chaos happens. The rapid cooling and decompression makes noise, a lot of noise. That’s the “blast” you hear when firing a gun.

How much noise is the gas blast? Even an unsuppressed .22LR pistol, at about 153 decibels, is louder than a jet taking off. A .45 ACP pistol shot can be over 160 decibels. Keep in mind that decibels are measured on a logarithmic scale, so just a three-decibel increase represents a doubling of sonic energy. Every decibel matters, so when silencer companies talk about lowering the noise of a shot by 20 or 30 decibels, that’s a really big deal.

What maketh less noise?

Since the most abusive noise is caused by the muzzle blast of expanding and cooling gas, that’s where suppressors work.

Just a like a car muffler, a suppressor keeps the hot compressed gasses contained until they have the opportunity to cool and expand a bit. The idea is that if you can lower both the temperature and pressure before letting those gasses interact with the atmosphere, the energy, and associated noise will be reduced. The closer you can get the muzzle gasses to the ambient atmospheric conditions before they exit, the lower the noise signature.

The best way to illustrate the sonic power of pressure differential is to fill up two balloons. Pop the first one with a pin. If it’s really full, it will make a loud noise and frighten the dog. The noise is certainly not caused by the pin. It’s caused by the rapid expansion of the pressurized air inside the balloon when the balloon’s barrier is suddenly broken. Take the second balloon, and allow the end to open, gradually letting the air out. There’s just a small hiss and no big noise. That’s because the interior pressure and exterior lack of pressure reach equilibrium gradually. Without a sudden release of pressure, there’s no bang.

Since a suppressor is fixed onto the muzzle end of a barrel, the gasses remained contained until they exit the muzzle of the suppressor device. You’ll notice that a suppressor is larger than the barrel of the gun, and that’s because the most effective part of a suppressor is the air inside. The more air space there is within the contained system, the more room there is for the muzzle gasses to expand and cool before they exit the suppressor. The inside is not just an empty cavity. Instead, the interior consists of baffles that redirect and swirl around those gasses, thereby allowing them to further dissipate heat and pressure before they finally make their way to the muzzle.

Some suppressor designs use a single piece of steel to create the interior baffles. You’ll see this type of construction on many .22LR suppressors. Others use a series of baffles that stack on top of each other like round Lego blocks. These stacked baffles are contained by a body tube that keeps everything inside. On many suppressors, you can remove the interior baffles or baffle assembly from the exterior tube for cleaning and maintenance.

Shouldst thou wet it?

You might have heard people talking about shooting suppressors wet. With many, but not all, pistol suppressors you can add a small amount of liquid into the blast chamber before shooting. The idea is that the fluid coats the interior baffles and helps cool those hot gasses more rapidly. More specifically, the hot gas contacts whatever ablative liquid or gel you use, and the heat turns it to vapor, thereby expending energy and cooling faster. The more the superheated gas cools inside of the suppressor, the lower the volume, and the less noise generated when those now cooler and less voluminous gasses exit the suppressor muzzle. At some point, the liquid is completely “burned up” and the suppressor reverts to its dry noise level. Using water in a pistol suppressor may get you 10-20 shots of enhanced performance before a refill is needed, but that all depends.

There are a few important things to understand before trying the wet method.

Never, ever, ever use a liquid in a rifle suppressor. There’s way too much pressure at play with supersonic rifle rounds, and the addition of fluid inside the suppressor body can turn your silencer into a grenade. Do people do it? Yes. Should they? No. Don’t risk it, use the wet method with pistol suppressors only and only when the manufacturer documentation specifically says that it’s OK to do so.

Whatever fluid you use, you’ll be wearing. Technically, you can use water, oil, wire pulling gel, or adult activity lubricants inside of your suppressor. Just be aware that when you pull the trigger, some of that material will come straight back at you through the action of your gun. Oil sounds like a great idea at first, until you acquire a light coating all over your face. This and convenience is probably the main reason people choose to wet their suppressors with water.

A little goes a long way. Most manufacturers that allow wet use suggest using only 5cc’s or less of liquid. More is not better as you’ll be wearing whatever liquid you pour in there. Also, you don’t want to create any possible obstruction to the bullet itself, even if it’s just liquid. Even a blob of gel can misdirect the bullet enough to cause a baffle strike. You definitely don’t want to risk that.

A popular wetting substance is wire pulling gel. Construction folks smear this around wire that they pull through building conduits to make it feed easier. Used on a suppressor, the gel stays in place on the interior surfaces better than water, so it’s less likely to drizzle out the muzzle end. Be sure to use a clear, water-based gel. Just add 5cc’s into the blast chamber, cover both ends of the suppressor, and shake it all around so the gel is distributed all over the interior baffles. When finished, look through the silencer to make sure no blobs of gel are in the path of the bullet.

To boost or not to boost, that is the question…

Many pistol caliber suppressors come with an option called a booster or Nielsen device. The purpose of these devices is to allow a semi-automatic pistol to complete its normal recoil operation when the suppressor in installed.

Modern pistols often use the Browning tilting recoil system. When the gun fires, the barrel moves slightly back and tilts muzzle upward to disconnect it from the slide. This allows the slide to continue backward to eject a spent cartridge and pick up a fresh one from the magazine.

The problem is that when you add a suppressor, you’re attaching a bunch of weight to the end of the barrel. More force is required to drag the barrel backward, and more is required to “lift” the suppressor as the barrel tries to tilt muzzle up.

A Nielsen device or booster separates the barrel and suppressor with a clever spring and pistol assembly. When the gun fires, the hot gasses press forward on the suppressor. The spring and pistol allow the suppressor to move forward independently of the barrel, so the barrel is temporarily disconnected from the weight of the suppressor. As the booster piston spring compresses, it helps pull the heavier suppressor back in the same direction as the barrel so the barrel is not having to do the extra work. Think of the spring and pistol assembly as a way to move the suppressor in the same direction as the barrel using gas and spring pressure.

The net effect of all this physics is that your semi-automatic gun will continue to function normally even with the added weight of a suppressor.

However, this booster assembly should only be used on host guns where the barrel needs to move backward under recoil. Fixed barrel guns like pistol caliber carbines or rifle calibers use a fixed mount to attach the suppressor to the barrel. Just remember, for a fixed barrel, used a fixed mount. For a moving barrel, use a booster.

What about ammo? Doesn’t supersonic ammo negate the whole suppression thing?

Contrary to internet myth, using supersonic ammunition is not as pointless as NFL kickoffs under the new rules. It’s true that any particular combination of gun and suppressor will be at its quietest when using subsonic ammunition. That’s because another of the three components of noise is eliminated in that scenario – the sonic boom of a supersonic bullet.

However, even when using supersonic ammunition, there are still big benefits to suppressor use. While there is still a small sonic boom, it’s moving rapidly away from the shooter. With the lower amount of blast and noise at the muzzle, the sound level is much, much lower from the shooter’s perspective. In a battlefield scenario, the suppressor also effectively masks the origination of the shot, so it becomes difficult to determine the location of the shooter. People downrange will hear the sonic crack of the bullet, but that’s about all. Use of a suppressor also reduces and smoothes out felt recoil, making the shooter more effective with accurate follow-up shots.

It’s for these reasons that companies make suppressors for rifle calibers like 5.56mm and .308. There are still plenty of benefits to be realized, even though the supersonic ammo will make its own little sonic boom.

There you have it, perhaps more than you ever wanted to know about how suppressors operate. If you’re interested in getting your own, check out the How to Buy resources at The Silencer Shop. They’ll walk you through the process so you can be shooting with a lot less bang in no time.