Re the headshot at Z313.
Camera running at 18.3 frames/sec.
If Hickey fired, then he fired at Z312.85 (based on 26 ft at 3251 fps = 0.008 sec = 0.15 frames, which is deducted from Z313).
Sound hits Zapruder at Z313.35 (based on 90 ft at 1100 fps = 0.082 sec = 1.50 frames, which is added to Z312.85).
The shockwave jiggle would be at Z314 (but there is zero camera jiggle at Z314)(there is camera jiggle at Z318 & Z319).
Zapruder's startle reaction camera jiggle would be at say 234 millisec, which is 4.28 frames, which is added to Z313.35 to give a camera jiggle at Z317.63 (& there is indeed a large [ear] camera jiggle at Z318 & Z319).
Zapruder saw JFK's head explode at Z313 -- & a startle camera jiggle due to what he saw could be expected at Z317.28 frames (so this [eye] jiggle too accords with the jiggle at Z318 & Z319).
Zapruder's voluntary reaction jiggle would be at say 970 millisec, which is 17.75 frames, which is added to Z313.35 to give an [ear] camera jiggle at Z331.10, or is added to Z313 to give an [eye] camera jiggle at Z330.75.
There is indeed a camera jiggle at Z331 & Z332 (which accords a little better with the expectation for the [eye] jiggle rather than the [ear] jiggle).
And, we know that Hickey fired a plurality of shots, probly starting before Z300, hence we can safely say that Zapruder reacted to what he saw [eye], rather than what he heard [ear].
If Oswald fired a shot-3, then he fired at Z310.75 (based on 266 ft at 2170 fps = 0.123 sec = 2.25 frames, deducted from Z313).
Sound hits Zapruder at Z315.25 (based on 270 ft at 1100 fps = 0.245 sec = 4.50 frames, added to Z310.75).
The shockwave jiggle would be at Z316 (but there is zero camera jiggle at Z316).
We have earlier said that Hickey's shots did not result in a shockwave camera jiggle, & Hickey was much closer to Zapruder than was Oswald, hence the lack of a shockwave jiggle for any of Oswald's shots should not come as a surprize. And indeed there was no significant camera jiggle of any kind tween Z198 & Z318, including Oswald's shot-2 which is generally agreed to have happened tween Z218 & Z224.
Zapruder's startle reaction to an Oswald shot-3 camera jiggle would be at say 234 millisec, which is 4.28 frames, which is added to Z315.25 to give a camera jiggle at Z319.53 (which would give an [ear] startle camera jiggle at Z320)(but the large camera jiggle was at Z318 & Z319)(so, if Oswald did shoot a shot-3, then the sound of the shot did not result in an [ear] startle camera jiggle).
However if an Oswald shot-3 caused the head explosion at Z313 then that of course would explain the [eye] startle camera jiggle at Z318 & Z319 (but Oswald did not shoot a shot-3).