Silencer Terms and Tech, Part 1

Hiram Percy Maxim, the son of Hiram Stevens Maxim—who invented the Maxim machine gun, is the father of the firearm silencer. An early advertisement for his Maxim Silencer Company explained that the hot propellant gases from discharging the firearm “are made to whirl around inside the Silencer,” and cannot leave the silencer until they have slowed down enough to not produce a loud noise. Although this explanation of silencer operation was first printed more than 100 years ago, it still correctly describes the function of all silencers today. Before the adoption of the National Firearms Act in 1934, Mr. Maxim sold a variety of silencer designs via the US mail, at a price range of $5.00 to $9.50, for those with deep pockets.

Original Maxim ad, click for full size image, courtesy of AAC

“But wait!” some say. “The correct term should be sound suppressor, because it is impossible to make any firearm truly silent.” Even firearms with the most advanced silencers available still make some noise when fired, so the point is well taken. However, the original inventor called his device a “silencer,” and federal and state laws universally call the device a “silencer,” so this article will refer to them as silencers.

Silencers consist of a few basic parts. The envelope is the cylindrical metal tube in which the other components are stuffed. Inside the envelope are the expansion chamber  and baffles. The expansion chamber is a relatively big empty space surrounding the muzzle, and the baffles are like coffee cups stacked on top of each other with a hole drilled through the middle of them for the bullet to pass through. This is where most of the “magic” happens within the silencer. Manufacturers competing against each other for the same exact application, will design very different baffle shapes and sizes. Finally, there is a cap at each end of the envelope, one with threads—or a quick detach adapter—to attach the silencer to the muzzle, the other with a simple hole for the bullet to exit the silencer on its way to the target.

When a bullet is fired, it leaves the muzzle of the gun and passes through the expansion chamber, where the propelling gas behind it expands from the diameter of the bore to fill the envelope. The expansion chamber takes a lot of abuse as it is the first silencer part to get hit by that hot gas. As the bullet continues to pass through the envelope, each baffle catches and diverts more and more of the gas, swirling it around, forcing it to slow down, and converting a lot of its energy into heat—which gets the silencer real hot, real quick. All of this reduces the sound made by the muzzle blast. It is possible to overwhelm a silencer by using sustained full auto fire. If the rate of fire is high enough, the gas from each successive shot stacks up inside the silencer and cannot dissipate into the baffle assembly. The sound of firing will become louder and more muzzle flash will be seen until the long full auto burst ends.

“Overwhelming” a silencer with sustained fire, image courtesy of Oleg Volk

“First round pop” is a problem for silencer manufacturers. Propellant gas from the first shot of a magazine ignites the oxygen in the air inside the silencer, creating extra noise. Follow-up shots fired quickly afterward do not have the same problem because the silencer is filled with propellant gas and air that has already been burned up. When firing stops for awhile and fresh air enters the silencer, first round pop will happen again when firing resumes. A large expansion chamber tends to contribute to a lot of first round pop, but a smaller expansion chamber decreases the overall efficiency of the silencer and can be harder on the silencer’s internal parts. Various manufacturers have different ideas about what compromise is best.

Many pistol caliber silencers are designed to be operated wet, meaning the silencer can be filled with a small amount of water before firing. Upon firing, the water vaporizes, assisting the baffles in slowing and cooling the propellant gases, and minimizing first round pop. A silencer filled with water also takes longer to get hot, since the water efficiently draws heat away from the silencer’s parts. There is no doubt that a pistol caliber silencer filled with water or gel is quieter than a dry silencer— for awhile. Some water is blasted out of the silencer by the pressure from each shot and the rest evaporates quickly from the intense heat, so the wet silencer quickly loses efficiency and subsequent shots get louder and louder. The other problem with running a silencer wet is that if the barrel is tilted up, water will run out the rear of the silencer and down the barrel of the firearm, potentially causing a barrel obstruction. If the barrel is tilted down, the water simply runs out the front of the silencer and the benefit of shooting wet is lost. Some shooters have begun to experiment with filling the silencer with a variety of oil or gel based products which stick to the guts of the silencer and won’t leak out. Silencers being used with centerfire rifle calibers should never be filled with water or gel.

More silencer terms and tech, including the Vietnam-era “hush puppy” and the Nielsen device, are found in part two, coming soon!

X-ray showing competing silencer designs
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