When a rifle bullet breaks the sound barrier why doesn't it make a loud boom?

Question

When the bullet leaves the barrel,the boom you hear; is that the sound barrier being broken?

Answer 1

Part of the sound that a rifle makes when you fire it is the sonic boom from the bullet passing through the sound barrier.

That is why a silencer works on a pistol, but not on a rifle. You could muffle the sound of the gas going bang, but you can't prevent the sonic boom, so it would be pointless.

Answer 2

A firearm is going to make several differant noises. the loud bang of the gases exiting the muzzle, action noises if it is a machinegun or semi-automatic, and a sonic boom if the bullet moves faster than about 1100 feet per second, or the speed of sound.

The muzzle blast is by far the loudest sound. The sound of the bolt slamming can be over 100 decibels all by itself. The sonic boom of the bullet (sounds like a whip snapping) adds little to the total noise.

Silencers (suppressors) actually can be useful on high powered rifles and pistols using supersonic ammo. When a bullet moving at supersonic speeds passes an object between the shooter and the target, the bullet flight noise will bounce off of the object and make it seem that the shooter is near the object the bullet passes.

Edited to add. The sonic boom is not very loud because the bullet is small and the amount of air displaced by its shockwave is also small, so not much noise. They are louder than subsonic bullets though.

Answer 3

Okay, most rifles, if you're firing super-sonic ammo, has already accellerated to the speed of sound by the time its left the barrel, as has already been said. And since the sound of the explosion is currently going on in your head, you miss the sonic boom. You can't tell the difference do to the excessive noise. After it leaves the barrel, there is another reason why you don't "continue" to hear the sonic boom. The sonic boom is a shock wave where the bullet is piercing the sound "in front" of it. The sonic boom travels with the bullet. So if you're standing in front of the path of the bullet, but off to the side (hopefully) you'll hear the sonic boom as it passes you by (hopefully not through you). It's like a jet plane. When it's traveling supersonic, you don't hear it until the shockwave passes you. It's like a boat traveling along the water. The sonic boom is the wake coming off the bow.

Answer 4

The speed at which the bullet leaves the barrel is called the muzzle velocity. This is usually measured in feet per second. The page below lists several muzzle velocity for different rifles and different ammunition loads. They range from 2050 to 3100 feet per second (fps).

The speed of sound is about 1025 fps. So these bullets are going 2 to 3 times the speed of sound. I think what you hear when a rifle fires is a combination of the "crack" noise made by the hypersonic bullet, and the "boom" made by the powder exploding.

Answer 5

If it is true, that the bullet is breaking the soundbarrier, then this should happen within the rifle already .... so the sound breaking and the chemical explosion in sum should make up the bang, which you hear when shooting.

But is an interesting question .... I never thought about this aspect and am curious if a more experienced physicist is supporting my point of view.

Answer 6

No, the boom is the explosion that accelerates the bullet. The sonic boom sounds like a loud "crack." This is why you'll hear that distinctive sound when most rifles fire (easier to differentiate from the shot itself a distance) and not when a pistol fires - as pistol rounds are typically subsonic.

Answer 7

It does. The crack of a rifle is due to both the sound barrier and escape of highly compressed gas.

Answer 8

thts wht you call an explosion, sound made from the gun powder inside the bullet, the extra bang sound comes from the shape of the gun cylinder...i saw this somewhere in discovery channel

Answer 9

Yes in fact you can purchase sub-sonic rounds for most applications that make very little noise.

Answer 10

yes