“Also, the killshot from the Zapruder film was fired from the front, and was not from a 6.5 Carcano.”
No. The entry wound in the back of JFK’s head, and is well known from the autopsy photos, with the bullet shattering inside the skull and blowing out the right side of his head.
JFK’s head goes backwards because that was the direction of the shot. The entry wound produces almost no energy transferred to the body. The exit wound is what causes the head to move backwards. Penn and Teller (of all people) demonstrated this by shooting bullets at melons, and seeing which direction they moved after the bullet hit them. The melons moved in the direction OF the shooter, not away from it.
The entry wound does nothing, the exit wound transfers kinetic energy to the body.
I’m arguing from memory based on the book I mentioned, which I haven’t read recently. But that’s the gist of it.
You can shoot a thousand melons and half will go one way, half will go another. I know; I’ve done it.