Can Andrew point out anything in the Z270-ish range of frames indicating
some kind of impact of a bullet hitting JC?
The sudden movement of JBC that begins at z271-272 and continues through z278 before he falls back. It is subtle but before he falls back onto Nellie he moves toward the front of the car without moving any part of his body to initiate this motion.
There is also a slight change in his hand position and the hat he is holding between z271 and z272.
There is also the odd lifting of JFK’s hair on the right side of his head that George Hickey observed at the time of the second shot (z273-277).
Finally, there is Wm Greer’s first turn around at around z280 which he said he did immediately after -“almost simultaneous” with- the second shot.