The Sonic Crack!

[Deker 3,478]

Anyone who has stood in the Butts at any decent range will tell you about the boom as the bullet flies over your head!

 

It is interestingly different to the boom you hear when you are actually firing the gun as the propellant bang is not part of the noise anymore!

[Alsone 789]

Alsone I am afraid you are wrong there is definitely a sonic boom/crack created for the entire time the object is supersonic. BTW I am a physicist

 

Oh OK then. Like I said, I'm not.

[Cliff Ray 185]

It's alright, if everyone was a physicist the world would be a very boring place

[Born Hunter 17,751]

It's alright, if everyone was a physicist the world would be a very boring place

 

Tell me about it!

[Cedric 132]

Wow! That stirred things up a bit ! Thanks for the answers.

 

The animation on Wikpedia shows the sound breaking wave/cone is continuous so I presume a rabbit passed by the bullet would hear the full crack, not a diminished one from 100 yards away.

 

Sometimes adjacent rabbits don't run at the sound of a shot, I wonder if they are confused by the directionality or the sheer volume of the sound.

[rimmer 33]

I`m with deker on this i do know a little about this subject and the sound is due to the pressure wave, which is pure at range and is a defined crack where as at the barrel its a more converluted sound contaminated with the ignition of the powder.

not sure about how well rabbits in other fields can locate the origins of the sound, the one in the cross hair certainly wont.

Edited March 19, 2014 by rimmer

[Bear1cat 4]

I have been in the butts at the far end of ranges.

The crack of the Bullet going overhead gives no indication of the direction it came from.

The thump that follows a second or so later which is the sound of the muzzle blast reaching you does.

[dadioles 68]

Part of the problem is one of perception.

 

People think of the bullet as "breaking the sound barrier", rather like smashing through an egg shell, a single event.

 

That is not what happens.

 

A bullet fired from a gun will accelerate while in the barrel but assuming a complete burn of the powder the bullet is decelerating as it leaves the barrel and continuing to slow down thereafter.

 

While in the barrel, the bullet is accelerated to a speed greater than the speed of sound and a pressure wave is built up which effectively travels with (behind) the bullet and is continuous. You will only hear a single crack of the sound (pressure) wave as it only passes over you once. Someone a few hundred yards away will also hear the crack, but it will be a "different" one that only they hear and so-on along the line until the bullet has slowed to subsonic speeds and the pressure wave has diminished.

 

There is, of course, the "bang" of the powder exploding and this can be reduced by the use of a moderator. The sonic boom is quite a different physical event and is heard later.

 

If you fire an hmr, for example, into soft earth or sand just a foot or so in front of the barrel, you will not hear the sonic crack as the pressure wave has not properly developed, with a moderator it is surprisingly quiet, rather like a subsonic .22

[rimmer 33]

Well thers 2 minutes I wont get back!

[dadioles 68]

I`m with deker on this i do know a little about this subject and the sound is due to the pressure wave, which is pure at range and is a defined crack where as at the barrel its a more converluted sound contaminated with the ignition of the powder.

not sure about how well rabbits in other fields can locate the origins of the sound, the one in the cross hair certainly wont.

 

You will have to read quicker rimmer - 2 mins......

 

My guess is that a rabbit or other animal would be unable to place the source of a supersonic crack, or at least not relate it to where the rifle is located. There is no real directional source it is "fuzzy" and more overhead than anything as it is generated by, and is a short distance behind, the bullet. They might all bolt down the nearest hole but I think it will be more "what the f..k was that" rather than "there is a bloke over there shooting at us". Maybe the flash and puff of smoke is the real give away.

 

Apart from the one that did not hear it because it is now dead and the sound has only just arrived, I wonder if the supersonic crack masks the subsonic bang as the powder ignites. Fire a moderated .22lr and a group of rabbits might momentarily look towards the source of the sound. I have never really thought about it with the hmr. Will take more notice next time I am out.

Edited March 28, 2014 by dadioles

[Born Hunter 17,751]

 

Apart from the one that did not hear it because it is now dead and the sound has only just arrived, I wonder if the supersonic crack masks the subsonic bang as the powder ignites. Fire a moderated .22lr and a group of rabbits might momentarily look towards the source of the sound. I have never really thought about it with the hmr. Will take more notice next time I am out.

 

 

The sound from the muzzle blast will arrive after the sonic crack, so probably not. Assuming the distance from the passing bullet to the rabbit is significantly shorter than the distance from the gun to the rabbit. In the rare circumstance of both sounds arriving at the rabbit simultaneously then I can believe that it would indeed make it difficult to discriminate the muzzle blast.