Subj:  Bullet strike photo evid                Section: The Back Room [1]
From:  Anthony Marsh (MA)       72127,2301     # 6047, 1 Reply 
  To:  Joe Knapp                70403,2231     Date: 13-Oct-93 10:44   

I can give you a few details off the top of my head and will try to copy
out more for you this weekend. The speed of sound at 12:30 PM CST on
11/22/63 was 1123 fps. That's about 65 degrees. You can also derive the
speed of sound from the acoustical analysis as other variables become more
narrowly defined.
I am confused by your statement that "Sounds, even supersonic shock waves
(once created) travel at the speed of sound (duh)." That use of "(duh)"
seems to imply that you know something which any idiot should know. I hope
you do know that supersonic shock waves do travel faster than the speed of
sound. That is why they are called supersonic. Figuring out the rate at
which the shockwave slows down is the same as figuring out the rate at
which the bullet slows down, which has already been calculated for the
M-C, until the bullet hits it target. After that the decay of the
shockwave is a little trickier to figure out and involves calculus. But
you can still use the ballpark figure for the rate at which the shockwave
slows down. It is close enough for our purposes. 
Naturally I believe the head shot came from behind Zapruder on the grassy
knoll, so he felt the shockwave before the bullet hit. But for the sake of
your argument, you can assume that the shockwave arrived at Zapruder very
shortly after the bullet hit if it came from the TSBD.
I can not agree with the idea that the bullet had to hit within Z-313. I
believe someone has done some calculations before (Alvarez?) which
indicate that the particles exploding from the head had a velocity which
worked backwards would start to exit the head before Z-313 started being
exposed. That's why I use the benchmark of Z-312.6 for the hit, just after
the shutter closed.
So, although I think the shot came from the grassy knoll rather than the
TSBD, I do not believe your logic can disprove the TSBD shot.
Tony