The propagation of Kaboom

[Charles Collins]

There appears to be some active members here who are experienced in some of the technical matters concerning the assassination. This thread is a request for assistance in understanding potential reasons why the sound of the first shot was reported by so many witnesses in Dealey Plaza to be a different (fire cracker) sound than the other two shots. Here is a link to a summary of gunshot acoustics by Robert C. Maher, Montana State University:

https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf


It is written in a manner which I think that most people can get a grasp on the basics of the physics of the sound of a high powered rifle. What remains a little mysterious to me however is how the shock wave propagates from the supersonic bullet. It is shown to be perpendicular to the angle of the shockwave cone. And when the microphone was placed behind the rifle, there was no sound of the shockwave at all, but the muzzle blast is still recorded.  My questions are:

1.  Does the shockwave sound behave differently than normal sound waves which are typically omnidirectional?

2. Does the perception of the shockwave sound depend upon being in a position in which its travel (perpendicular to the shockwave cone) would hit the person?


 That is the way that it appears to be to me based on what is in the above referenced summary. Please let me know if you have the answers to my questions. Thanks.

[Jack Nessan]

There appears to be some active members here who are experienced in some of the technical matters concerning the assassination. This thread is a request for assistance in understanding potential reasons why the sound of the first shot was reported by so many witnesses in Dealey Plaza to be a different (fire cracker) sound than the other two shots. Here is a link to a summary of gunshot acoustics by Robert C. Maher, Montana State University:

https://www.montana.edu/rmaher/publications/maher_aac_0406.pdf


It is written in a manner which I think that most people can get a grasp on the basics of the physics of the sound of a high powered rifle. What remains a little mysterious to me however is how the shock wave propagates from the supersonic bullet. It is shown to be perpendicular to the angle of the shockwave cone. And when the microphone was placed behind the rifle, there was no sound of the shockwave at all, but the muzzle blast is still recorded.  My questions are:

1.  Does the shockwave sound behave differently than normal sound waves which are typically omnidirectional?

2. Does the perception of the shockwave sound depend upon being in a position in which its travel (perpendicular to the shockwave cone) would hit the person?


 That is the way that it appears to be to me based on what is in the above referenced summary. Please let me know if you have the answers to my questions. Thanks.

The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.

The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.

There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.

[Charles Collins]

The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.

The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.

There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.

The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.


I agree, however that is why I believe that the sniper waited until the limo was past his window. An ambush from behind is his best bet to be able to get a few shots off before being detected. I also believe that basic military training and a military mindset would help a potential sniper instinctively know this.

[Dan O'meara]

The first shot was taken by Oswald with the barrel of the rifle retracted inside the room. The second shot he had the rifle extended outside the window. A number of TSBD employees inside the building only recall one shot and also the dust on Bonnie Ray Williams from the concussion of the rifle blast would be explained by the rifle being fired with the barrel being completely inside the room.

The Secret Service and Police were looking at the windows of the buildings looking for a sniper. A protruding rifle barrel would have brought an immediate response.

There would be a definite sound difference between the two different positions of the rifle. The second shot would most likely have a different echo component to it with the barrel extended outside the window.

This is, more or less, what Amos Euins witnessed.
At the first shot he states just a small part of the barrel was sticking out of the window:

Mr. Specter: And how long was the piece of pipe that you saw?
Mr. Euins: It was sticking out about that much.
Mr. Specter: About 14 or 15 inches?

After the first shot the shooter moves forward exposing more of the rifle:

Mr. Euins: Well, when he stuck it out, you know--after the President had come on down the street further, you know he kind of stuck it out more, you know.
Mr. Specter: How far was it sticking out of the window would you say then, Amos?
Mr. Euins: I would say it was about something like that.
Mr. Specter: Indicating about 3 feet?
Mr. Euins: You know--the trigger housing and stock and receiver group out the window.
Mr. Specter: I can't understand you, Amos.
Mr. Euins: It was enough to get the stock and receiving house and the trigger housing to stick out the window.

[Charles Collins]

This is, more or less, what Amos Euins witnessed.
At the first shot he states just a small part of the barrel was sticking out of the window:

Mr. Specter: And how long was the piece of pipe that you saw?
Mr. Euins: It was sticking out about that much.
Mr. Specter: About 14 or 15 inches?

After the first shot the shooter moves forward exposing more of the rifle:

Mr. Euins: Well, when he stuck it out, you know--after the President had come on down the street further, you know he kind of stuck it out more, you know.
Mr. Specter: How far was it sticking out of the window would you say then, Amos?
Mr. Euins: I would say it was about something like that.
Mr. Specter: Indicating about 3 feet?
Mr. Euins: You know--the trigger housing and stock and receiver group out the window.
Mr. Specter: I can't understand you, Amos.
Mr. Euins: It was enough to get the stock and receiving house and the trigger housing to stick out the window.

That’s interesting, thanks. The sound from a high powered rifle consists of the sonic wave created by the supersonic bullet and the muzzle blast that is created by the gases and other materials exiting the muzzle behind the bullet. I am mostly interested in how the sonic wave is propagated. Apparently it’s propagated differently than normal sound waves. I believe that even if just the muzzle end of the barrel is exposed outside the window opening, that the sound should be similar to a situation where more of the rifle is exposed.

[Charles Collins]

Okay, I have read a little bit more and considered this question quite a bit more. And I do believe that my initial thinking is correct. I believe that the sonic shock wave behaves differently from normal sound waves. A simplified analogy would be the wake of a boat traveling on the surface of a body of water. The most obvious difference being that the surface of the water is essentially a flat, one-dimensional plane. Whereas a supersonic bullet usually travels in a 3-dimensional air space. But I believe that the basic behavior (aka:its propagation) of a shockwave from a supersonic bullet is similar to the boat wake but the shockwave is 3-dimensional. Does this make sense? And does anyone disagree and have an alternative explanation?

[Brian Roselle]

I’m catching up on this thread, another large honey-do project has me distracted.

I would agree with these comments that the sound of the first shot might sound somewhat different based on the gun position. As I recall, and maybe it was in Max Hollands National Geo video, that an early shot would require a steeper downward aim, and that would require putting the end of the barrel further back, perhaps in or near the plane of the window rather than sticking out much. I also seem to recall that Elsie Dorman mentioned the first sound being different and like some of it was actually coming from inside the building.

I’m not an expert in ballistics, but did look at shock waves a little bit during an earlier discussion with someone on another forum, so I’ll try to share what I know (or at least think I know) related to your questions. Others with expertise can probably correct or clarify any issues.
From what I understand, I think you basically have it right in what you have described, and that the shock was propagates out as sort of a straight line wave, but in three dimensions, along the sides of an expanding cone as it radiates out.

So the differences as I understand it is that in 3 dimensions the (point source) muzzle blast expands as a sphere, were as the components of the shock wave are constantly created along the path of the bullet, and the sound at the point of creation also radiates as a sphere, but due to the bullet movement the sounds created superimpose creating the surface of a cone which builds up the strong shock wave that radiates out at an angle from the bullet path determined by bullet speed (Mach value).

Comparatively, the way I understand it, is that the muzzle blast is from the hot gasses exiting the barrel which disrupts the air at a concentrated point area at the muzzle exit, the sound source. As you said, the sound propagates omnidirectional from there, basically as the surface of an expanding sphere. The sound Intensity (as power/unit area) decreases as 1/r^2 from the source since the surface area of the expanding sphere expands with r^2. Where r is the distance from source i.e. the sphere center.

The shock wave is created as the bullet constantly sheds off sound (a pressure wave) as the bullet travels and is seen as the angle of a cone relative to the bullet path, the angle depends on how fast beyond the speed of sound the bullet is going. The direction of shock wave propagation is perpendicular to the cone surface as it grows. The base of the expanding cone starts at the muzzle with the bullet moving forward and the wave goes mostly forward and out to the side from there, so behind the shooter there may be no shock wave encountered. I think the sound heard should be slightly different than a muzzle blast because of how the sound is created, and at its creation point along the path of the bullet the shock wave's net initial intensity may be lower than the initial intensity of the muzzle blast when one is closer to the gun (but intensity differences change with distance) and is probably at a higher frequency, hence the crack. The perceived direction of source for a muzzle blast would be directed towards the sounds source, the muzzle, and the shock wave would seem to radiate from a direction that is perpendicular to its source, the cone formed along the bullet path, which in not necessarily towards the gun. Being able to discern two separate sounds would depend on their arrival time to one's ear, which would probably need to be greater than 50-80 ms, so being able to hear two distinct sounds vs one compounded sound would also depend on direction and distance that one was positioned from the gun.

The boat wave is a good example of the shock type wave in two dimensions. Rotate that V-shape wake shape in 360 degrees around the boat path and you would have a “cone” shape. Maybe that’s what a fast submarine leaves behind?

I struggle with explaining stuff, so let me know if something seems unclear or not in agreement with the material you have seen.

[Charles Collins]

I’m catching up on this thread, another large honey-do project has me distracted.

I would agree with these comments that the sound of the first shot might sound somewhat different based on the gun position. As I recall, and maybe it was in Max Hollands National Geo video, that an early shot would require a steeper downward aim, and that would require putting the end of the barrel further back, perhaps in or near the plane of the window rather than sticking out much. I also seem to recall that Elsie Dorman mentioned the first sound being different and like some of it was actually coming from inside the building.

I’m not an expert in ballistics, but did look at shock waves a little bit during an earlier discussion with someone on another forum, so I’ll try to share what I know (or at least think I know) related to your questions. Others with expertise can probably correct or clarify any issues.
From what I understand, I think you basically have it right in what you have described, and that the shock was propagates out as sort of a straight line wave, but in three dimensions, along the sides of an expanding cone as it radiates out.

So the differences as I understand it is that in 3 dimensions the (point source) muzzle blast expands as a sphere, were as the components of the shock wave are constantly created along the path of the bullet, and the sound at the point of creation also radiates as a sphere, but due to the bullet movement the sounds created superimpose creating the surface of a cone which builds up the strong shock wave that radiates out at an angle from the bullet path determined by bullet speed (Mach value).

Comparatively, the way I understand it, is that the muzzle blast is from the hot gasses exiting the barrel which disrupts the air at a concentrated point area at the muzzle exit, the sound source. As you said, the sound propagates omnidirectional from there, basically as the surface of an expanding sphere. The sound Intensity (as power/unit area) decreases as 1/r^2 from the source since the surface area of the expanding sphere expands with r^2. Where r is the distance from source i.e. the sphere center.

The shock wave is created as the bullet constantly sheds off sound (a pressure wave) as the bullet travels and is seen as the angle of a cone relative to the bullet path, the angle depends on how fast beyond the speed of sound the bullet is going. The direction of shock wave propagation is perpendicular to the cone surface as it grows. The base of the expanding cone starts at the muzzle with the bullet moving forward and the wave goes mostly forward and out to the side from there, so behind the shooter there may be no shock wave encountered. I think the sound heard should be slightly different than a muzzle blast because of how the sound is created, and at its creation point along the path of the bullet the shock wave's net initial intensity may be lower than the initial intensity of the muzzle blast when one is closer to the gun (but intensity differences change with distance) and is probably at a higher frequency, hence the crack. The perceived direction of source for a muzzle blast would be directed towards the sounds source, the muzzle, and the shock wave would seem to radiate from a direction that is perpendicular to its source, the cone formed along the bullet path, which in not necessarily towards the gun. Being able to discern two separate sounds would depend on their arrival time to one's ear, which would probably need to be greater than 50-80 ms, so being able to hear two distinct sounds vs one compounded sound would also depend on direction and distance that one was positioned from the gun.

The boat wave is a good example of the shock type wave in two dimensions. Rotate that V-shape wake shape in 360 degrees around the boat path and you would have a “cone” shape. Maybe that’s what a fast submarine leaves behind?

I struggle with explaining stuff, so let me know if something seems unclear or not in agreement with the material you have seen.

Thanks Brian, your description does appear to me to be what I obtained from the Montana State University Summary and another source which was just some comments on another forum. If I understand the particulars of the speed of the Carcano bullet, it is approximately Mach 2. So using the formula in the MSU Summary, I came up with an angle of 30-degrees from the path of the bullet to the cone of the shockwave. Hopefully that is a reasonable approximation of the angle at the initial muzzle velocity anyway.