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Silence and the Speed of Sound

We’ve all seen it in movies. An elite force of commandos, drug cartel hit men, or spies, attacks a well-fortified position, usually at night. They pick off sentries with their silenced weapons and the other inhabitants of the premises are unaware of their comrades’ demise. This is aptly called fiction because it’s impossible.

How are writers of books, movies, and TV creating a false reality? Partly because
even among experienced shooters, the percentage that has actually fired a “silenced” weapon is very small because the federal restrictions on silencers are equal to those on fully automatic machine guns. In other words, too tight and too expensive for most of us to navigate. It costs $600 in federal tax to register a silencer and enough paperwork to make even a bureaucrat cringe. Consequently, writers and producers have little to no experience with this device and have, thus, created a mythological product based almost entirely on its name and what they think it means.

How did this happen? A century ago, Hiram Maxim, the inventor of the Maxim machine gun, arguably the single weapon most responsible for the British holding onto their empire as long as they did, invented the “silencer.” That was his name for his product. Maxim knew that his product did not silence a gunshot, but he chose the name because it was good for marketing. That was a good decision because he sold a lot of “silencers.”

The correct term for this device is “suppressor.” It suppresses sound; it does not eliminate it. Very briefly, a suppressor is a tube that fits to the muzzle of a gun. The tube contains either baffles or some sound-deadening material. The purpose is to stretch out the sound of a bullet’s explosion, softening it from a sharp “crack” to more of a whooshing noise. Is the result silent? No. In any environment other than a busy city or a war zone, you would hear the whooshing noise. In an ambush scenario on a quiet night, the very first suppressed shot would alert the defenders.

Worst of all in ignoring physical reality is the silenced sniper rifle. These things pop up all over the mystery and thriller landscape. They are used when an assassin wants to kill someone from a distance so that the assassin can get away without detection. Prepare yourself for the shock: this scenario is also impossible!

To explain this, first consider that a rifle shot is composed of not one, but two sounds. The first is the sound of the explosion, which can be suppressed to a level that would usually not be noticed in an urban environment. The second sound is the sonic boom the bullet makes. No, it doesn’t sound like a jet breaking the sound barrier. It’s more like the sound of a whip cracking – roughly the sound of a firecracker. (The reason a whip “cracks” so loudly is because the tip of the whip breaks the sound barrier.) This tiny sonic boom cannot be suppressed. It trails behind the speeding bullet until the bullet falls below the speed of sound.

For perspective, the speed of sound is roughly 1,135 feet per second (fps) with some variation for temperature, humidity, and altitude. Many handgun loads propel a bullet faster than sound. All rifles loads do. High-powered rifle bullets travel from 2,000 fps to over 4,000 fps. See the problem? The fictional sniper’s bullet itself is not silent. Far from it. The sound of a bullet traveling at Mach 2 or 3 is almost equal to the sound of the explosion that launched that bullet.

I’ve had writers argue that it’s possible to make a rifle fire a subsonic bullet by reducing the powder charge. This is true. However, getting a rifle to fire a bullet at subsonic speeds nullifies the purpose for using a rifle in the first place: to reach out over a great distance with power and accuracy. To get the rifle bullet subsonic, you would essentially convert the rifle to a heavy handgun. A long-distance shot would be impossible.

I’ve read innumerable situations where a novel’s hero pursues a bad guy who is armed with a high-powered rifle. Inevitably there’s a scene where the bad guy sees the pursuing hero and fires a shot at him that narrowly misses. The hero hears the bullet “whiz” or “buzz” past his head. Angry hornets are frequently referred to.

Remember the speed of sound? The hero wouldn’t hear anything until the bullet was well past his head. Then he would hear a sound like a firecracker.

Unless it hit him. Then he wouldn’t even hear the shot that killed him.

Matthew Bayan is a writer and a firearms expert. Learn more at www.matthewbayan.com.