This isn't rocket science. I revisited the study myself and found the film speed created too much motion blur to claim the head moves forward.
OIC. The "revisit" of "the study" is your own. So then, where do we find this study of yours, it's assumptions, it's calculations, it's results, and it's conclusions? If nothing else, it should be entertaining.
Also, any detectable forward motion is minuscule if it only transpires over 2 frames @ 1/18 frames/sec and can't be attributed to anything. Besides, are you claiming that a tiny bit of forward motion negates back and to the left?
The collision of bullet on body is completely over by the end of frame 313. All of the momentum has been transferred. All of the acceleration caused by the impact has happened. Any change in motion seen between z313 and the succeeding frames is due to some other force being applied to JFK's body. Any physicist will tell you this. JFK's head is fairly still up to frame 312, accelerates forwards between 312 and 313, the accelerates backwards in the frames just after 313. Whatever caused the backward motion, then, cannot have been caused by the bullet that created the ugly havoc seen in frame 313. Any physicist will also tell you this.
All the head motion could have been caused by the frangible bullet, which did not come from behind. MCs don't fire dumdum bullets.
"Could have been caused." Nice weasel wording at a time you really need something really concrete in order to be taken seriously.
You need to understand what a "frangible" bullet it vis-a-vis a "dumdum" bullet. The former is made from compressed powder that is weakly bonded together so that it shatters on impact. The latter is, strictly speaking, an early version of the .303 British round made at the Imperial arsenal in Dum-Dum India. It was identical to the early .303 FMJ bullets, except that the jacket was open at the tip. That is, a Dum-Dum bullet was a early soft-nosed bullet. And yes, you can get soft-nosed ammunition for the Carcano:
https://www.ammunitiontogo.com/index.php/cName/65-carcano-soft-pointYou also need to explain why you think a "frangible" bullet had to have been used. Edgewood Arsenal and John Lattimer have independently demonstrated that WCC 6.5mm FMJ bullets will fragment when they hit a human head, and create nasty, explosive wounds in the process. For that matter, 5.56 NATO is (in)famous for it's tendency to fragment while passing through soft tissue, even when it doesn't hit any bone. Dr ML Fackler pointed out that the Bundeswehr's steel-jacketed 7.62x51 bullets will do the same, just bigger.
Go ahead and post the animated GIF of frames 312 and 313 and show us the forward head motion over .05 secs and back up your claim that only 1 shot came from behind. I will show you why you are FOS.
Apparently, you're too lazy to look for yourself. Someone else already put up a couple. But I can drop a couple more:
LOL. An amateur says what?
Ameteurs say things like "plasma" and "frangible bullet"