The propagation of Kaboom

[Jack Nessan]

The principal reason for me to begin this study is to explore a possible reason that many witnesses said the first shot sounded different than the other two shots. Some have suggested that the second two shots had the distinctive sharp crack of a high powered rifle but that the first shot sounded more like a firecracker or backfire. The shockwave created by the supersonic bullet is a big part of why the high powered rifles have the distinctive sharp crack sound. The shockwave is propagated much like a boat wake on the surface of a body of water (but in three dimensions). If a motor boat were to stop or slow down below "wake speed" a significant wake is no longer created. The same thing happens with a supersonic bullet (and it's shockwave) that stops or is slowed below the speed of sound.

I have taken Don Roberdeau's map and drawn some lines representing the various scenarios that I believe might have taken place in Dealey Plaza on 11/22/63. The first such image represents what I believe to be a rough idea of the propagation of the shockwave from a bullet that hits the mast of the traffic light in front of the TSBD.




The yellow outline represents the limits of the area on the ground that I believe would be affected directly by the shockwave of a bullet that hits the mast of the traffic light and is slowed below the speed of sound at that point. I calculate this area to be roughly 25,594 square feet.

The other scenario diagrams that I have prepared will follow as time permits.

The HSCA studied sounds and sound waves. Their study is under Analysis of Earwitness reports.

https://www.jfk-assassination.net/russ/jfkinfo/jfk8/sound2.htm

[Brian Roselle]

I think that diagram looks pretty good, those yellow lines look close to perpendicular to the cone surface and if the bullet and/or its fragment(s) all went subsonic at the tip of the red cone as drawn, then this diagram looks pretty representative of what I would expect to happen relative to a shock wave, and anyone to the right of the two angled yellow lines would likely not encounter any shock wave from such a shot.

I haven't checked out the reference link Jack just posted, it may provide some further insight.

[Charles Collins]

The HSCA studied sounds and sound waves. Their study is under Analysis of Earwitness reports.

https://www.jfk-assassination.net/russ/jfkinfo/jfk8/sound2.htm

Thanks Jack, I am interested in this because it contains some of their testing within Dealey Plaza. I am certainly not any kind of expert. But I am glad to see, at first glance, that my understanding of the basics of how the shockwave propagates agrees with what they describe. And it is interesting to see that their description of the loudness of the shockwave relative to the loudness of the muzzle blast indicates that they are both very loud. I will be interested to see how much the window opening might have muffled the muzzle blast if the rifle was completely inside the window. However, I don’t believe that the shockwave would have also been muffled because it is created by the supersonic bullet as it travels along its path. Therefore it seems to me that the first shot would have sounded very short (1-ms) and sharp (if the muzzle blast was muffled to any great extent). On the other hand, that shortness might be a possible reason that some witnesses apparently never recognized the first shot. This gets complicated very quickly. And these simplified diagrams I am creating are a very basic attempt to help visualize only one of the several aspects involved in the full picture.

[Charles Collins]

I think that diagram looks pretty good, those yellow lines look close to perpendicular to the cone surface and if the bullet and/or its fragment(s) all went subsonic at the tip of the red cone as drawn, then this diagram looks pretty representative of what I would expect to happen relative to a shock wave, and anyone to the right of the two angled yellow lines would likely not encounter any shock wave from such a shot.

I haven't checked out the reference link Jack just posted, it may provide some further insight.

Thanks for the input. I’m glad to know someone thinks along the same lines as I do. Yeah, the link Jack provided looks at first glance to be a worthwhile read.

[Charles Collins]

Here is another diagram showing a missed first shot hitting the pavement near the JFK limo around the Z133 area. If this scenario were to be correct, I believe that the bullet could conceivably ricochet off the pavement and continue on below the speed of sound to the areas of the mark around the sewer manhole cover and/or the curb near Tague's position.




I calculated the area depicted by the yellow outlines to be roughly 33,975 square feet of the ground which would be directly affected by the shockwave. A significant but not huge difference from the 25,594 square feet depicted in the scenario of the bullet hitting the mast of the traffic light.

[Charles Collins]

This diagram suggests the area (outlined in yellow) of the ground in Dealey Plaza that might be affected directly by a scenario of a second shot which hits JFK and JBC around the Z224 timeframe. Please take note of the vastly larger area affected as compared to either of the first shot scenarios diagramed and posted earlier in this thread. Of particular significance is the increased number of affected witnesses who's accounts we are familiar with.




The calculated area affected directly by a shockwave from this shot is roughly 86,456 square feet. This is over 2.5 times as many square feet as the larger area of the two first shot scenarios posted earlier in this thread. And it contains vastly more witnesses who wouldn't have been directly affected by the shockwave of either of those two first shot scenarios but would be affected by this shot in this scenario. It seems reasonable to me that this could be a major reason the two shots reportedly sounded different to so many witnesses.

[Charles Collins]

This diagram depicts the area of the ground in Dealey Plaza that might be directly affected by the shockwave of a bullet which hits JFK in the head around the Z313 timeframe. It is significantly larger than the affected area of the second shot scenario posted earlier in this thread. And even more witnesses would be directly affected.





The calculated affected area is roughly 108,788 square feet. This is well over 3-times the affected area of the largest of the two areas affected in the two first shot scenarios posted earlier in this thread. The same reasoning as stated in the second shot scenario applies to this scenario as to why I believe this to be a significant possible reason for the first shot to reportedly sound different than the last two shots.

[Charles Collins]

I found a cool photo by NASA of a shock wave by a supersonic bullet. Here’s a link to the webpage:

https://www.nasa.gov/mission_pages/galex/20070815/f.html


Near the bottom of the NASA webpage there is a link to a high resolution photo of this.


Edit:

And a very cool video showing some shock waves and muzzle blasts: