# The Naked Scientists Forum

### Author Topic: Why does a ricocheting bullet make the sound it does?  (Read 7995 times)

#### chris

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##### Why does a ricocheting bullet make the sound it does?
« on: 14/08/2012 11:50:17 »
When a bullet bounces off a wall or another hard object it produces a very distinctive whining noise. Why?

#### Lmnre

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #1 on: 14/08/2012 21:39:55 »
A "rifled" barrel means a barrel that has grooves that twist around the internal surface of the barrel that cause a bullet traveling down it to spin (like a gyroscope) to stabilize its orientation as it passes through the air once it leaves the barrel (otherwise it might tumble, which causes it to lose speed more quickly and to go astray and lose its accuracy). All sorts of guns have rifled barrels ... pistols, rifles, cannons, etc.

When a bullet hits a surface at a non-90° angle (ie, skims a surface), the tip may be pushed to the side and/or upward, but the bullet still has the momentum to spin about it's original axis. So now the bullet is wobbling, and this wobbling creates the distinctive "ricochet" whining sound.

For example, a bullet leaving a barrel with a "1:24" twist (that is, 1 turn in 24 inches) will cause the bullet to spin one turn for every 24 inches (or two feet) of travel. If it's traveling at 3,200 feet per second, then it's spinning at 1,600 revolutions per second. If it ricochets, it would wobble at 1,600 turns per seconds, which should produce a ricochet whine at 1,600 cycles per second (that is, 1,600 Hertz).

#### chris

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #2 on: 15/08/2012 13:40:36 »

So does this mean that only rifle bullets (or at least bullets exiting a rifled barrel) should ricochet? And therefore are the old John Wayne westerns showing gunslingers shooting at each other along canyons and gorges using revolvers - the action punctuated by obligatory ricochet noises - actually wrong or unlikely?

#### Lmnre

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #3 on: 15/08/2012 22:12:12 »
Yes, only bullets from a rifled barrel.¹ The "western" genre of movies typically portray circumstances that would have occurred from the American Civil War to World War One.² During this time period, the firearm manufacturing abilities were such that most or all firearms were made with rifled barrels, and so, their bullets had the ability to ricochet.
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¹ Or at least the bullets must be spinning. For example, back in the 1800s, Smith & Wesson experimented with what we would now recognize as a hand-held rocket launcher — a pistol with a smooth barrel that launched bullets that were miniature rockets with canted nozzles that imparted a spin to the bullet as they also pushed the bullet down the barrel. Here's a modern version of this idea.

² As for "western" genre activities in real life, in 1916 through 1917, US General "Black Jack" Pershing led the Mexican Punitive Expedition into Mexico to attempt to capture Mexican revolutionary Pancho Villa who had conducted guerrilla activities near the American border, most notably his raid on Columbus, New Mexico.

#### chris

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #4 on: 15/08/2012 22:40:14 »
Fascinating; so how was the benefit of rifling discovered, and when?

#### Lmnre

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #5 on: 16/08/2012 17:47:26 »
According to this source,
Quote
a lot of the early rifling development came from German speaking areas [of Europe]. The Germans already had a history of manufacturing crossbows that would spin their bolts in flight (either by shaping the arrow head, arranging the feathers of the arrow slightly off center, or by passing the arrow through a tube with grooves in it to impart spin), so they were aware of the basics of rifling and its benefits, even before they started manufacturing firearms.

#### RD

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #6 on: 16/08/2012 18:12:00 »
rifling is not necessary for the ricochet noise, nor is a rifle, it can be produced with one of these ...

https://en.wikipedia.org/wiki/Slingshot

Some of the translational energy of the projectile (a stone) can be converted into high-speed rotation when it hits a hard surface at an angle.

Air resistance will slow the rotation of the projectile and cause the pitch to drop.

http://www.freesound.org/people/cedarstudios/sounds/148833/

Depending on your position there could be a Doppler shift in the frequency of the sound as the spinning projectile passed by.
« Last Edit: 16/08/2012 23:56:48 by RD »

#### William McCormick

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #7 on: 16/08/2012 22:54:05 »
A subsonic round will not create that sound unless it does spin. The other is the super sonic noise created by the round, whether it is wobbling or not.

Usually when a bullet hits a solid object it starts to tumble, that will give you the wild ricochet sound that is very familiar, even from a subsonic round. The bullet is actually tumbling end over end, so as each end comes around into the direction of travel, the velocity is increased, and you get that varying pitch sound.

http://www.rockwelder.com/military/Ruger.wmv

This kind of shows, what I was saying.

Slingshots are amazing, they are "modern" subsonic, but the slingshot often spins the object they fire, causing supersonic effects. Years ago super sonic was considered around 320 feet per second. Some sound is traveling at that speed at certain humidity. So very safe plane manufacturers would warn of super sonic effects over 240 miles an hour. Especially for Navy planes. And rightly so.

Sincerely,

William McCormick

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##### Re: Why does a ricocheting bullet make the sound it does?
« Reply #7 on: 16/08/2012 22:54:05 »