Suppressor (Silencer) Fitted Rifle in the Dal-Tex Building?

[Bob Prudhomme]

The Supersonic Crack

Any projectile moving through the air at a velocity greater than the speed of sound (332 to 340 m/s or 1,089 to 1,114 fps in dry, 18 C or 65 degree F air, depending on who one listens to) will create a supersonic crack. Temperature, humidity and atmospheric pressure variations play a role in raising or lowering the speed of sound by a small percentage. In a firearm which lacks a substantial muzzle report (being fired over an open field) the sound resembles the loud tearing of a bed sheet.

Two sounds are actually created, one from the front of the bullet, and one from the rear. Near trees and buildings the sound waves come back as a distinct crack or pop each time the speeding bullet passes some object with a vertical, reflective surface. Once the muzzle report has been diminished the supersonic boom becomes dominant. Curiously, the sounds will now appear to come from the target area, rather than the rifleman's position. Sound moves through our atmosphere at a relatively fixed rate. A sound wave will typically strike one ear a bit before the other.

The human brain is capable of detecting the difference in time between sound impacting one ear and then the other in an increment of as little as one/six-millionth of a second. With time and practice we soon learn to use this ability to pinpoint the source of a sound very accurately. Because a suppressed muzzle report is relatively quiet, the uninitiated will automatically home in on the loudest sound, which in this case is a sonic boom reflecting from the target area. The intense, sharp sound of the bullet's passage will seem much louder than the muzzle report to someone close to the flight path. Indeed, a rapidly moving .308 bullet will sound louder than a .22 LR pistol, to someone who is positioned a few feet from its flight path.

http://www.silencerresearch.com/sound_su...rifles.htm

http://www.prayer-man.com/sniper-positio.../#lightbox[group]/0/

[Bob Prudhomme]

https://www.youtube.com/watch?v=n0cFOJU0...e=youtu.be

Video of suppressor completely eliminating muzzle blast but not the sound of the bullet breaking the sound barrier. Note how this sonic boom continues to return to shooter well after the shot was fired.

[Bob Prudhomme]

"Curiously, the sounds will now appear to come from the target area, rather than the rifleman's position."

Does this explain why the majority of witnesses heard all of the shots, and not just the final shot, originating from toward the Grassy Knoll?

[Drew Phipps]

Some of the witnesses, at least, were able to identify gunshot noises by the muzzle blast, because they would have been too far from the path of the bullet to hear the much-less-loud subsonic crack. I am reminded, that the first report heard by many ear-witnesses was misidentified as a firecracker, which seems less likely if the full muzzle blast noise was also present. The problem with the "echo theory" explaining why 20 cops converged on the grassy knoll, is that Chief Curry ordered them there...and since Chief Curry was on the opposite side of the target from the most likely shooter(s), the supersonic crack would have originated from north-ish and reverberated from the overpass itself, not the fence on the knoll.

Do you agree, Bob, that there is good evidence for more than one type of weapon being fired?

[Bob Prudhomme]

Some of the witnesses, at least, were able to identify gunshot noises by the muzzle blast, because they would have been too far from the path of the bullet to hear the much-less-loud subsonic crack. I am reminded, that the first report heard by many ear-witnesses was misidentified as a firecracker, which seems less likely if the full muzzle blast noise was also present. The problem with the "echo theory" explaining why 20 cops converged on the grassy knoll, is that Chief Curry ordered them there...and since Chief Curry was on the opposite side of the target from the most likely shooter(s), the supersonic crack would have originated from north-ish and reverberated from the overpass itself, not the fence on the knoll.

Do you agree, Bob, that there is good evidence for more than one type of weapon being fired?

Hi Drew

You have to understand that I am only discussing the first shot as being from a suppressed rifle. The last shot does not seem to have been from a suppressed weapon, and Curry, or someone near him, may have heard this shot from the Grassy Knoll. If you recall, a motorcycle cop was supposed to have raced up and given him the news of the shooting. Could this cop have been near this last shot?

What makes you believe the bystanders on either side of the street were too far away from the path of the bullet to be able to hear the "crack" of the sonic boom? If you watch the video I posted, you can hear the sound of the sonic boom returning from down range for several seconds. These witnesses would have heard the "crack" plus the echo of it as the bullet passed by every vertical reflective surface near its path. These witnesses, seen in Altgens 6, could very well have heard the "crack" without showing startle reactions, simply because the sonic boom is not as loud as a 140 decibel muzzle blast. However, any muzzle blast at all would have given away the location of the shooter. As there were, in 1963, suppressors capable of eliminating 100% of a muzzle blast, I'm willing to bet there was no muzzle blast from the first shot.

Yes, there were different weapons being fired in Dealey Plaza that day. Several witnesses reported that the last shot was much different than the first.

[Drew Phipps]

I wasn't limiting myself to ear-witnesses on either side of Elm. There were ear-witnesses further back in the motorcade, and on both sides of Houston. Many of them would not have been situated to hearing gunshots echoing from the fence on the knoll (as opposed to some other hard surface in the Plaza). Not to mention the dozen or so Sherriff's Deputies that were "standing down" outside the Criminal Court building.