As far as Kennedy's head snapping back, when you watch a cleaned-up version of the Zapruder film, you can see the bullet clearly striking him in the back of it but not cleanly, since the limo was rounding a curve. His head very quickly snapped forward and then back, which is what most people see.
Watch it here, especially in slow motion:
You are assuming that the first shot was fired as the limo was rounding the street onto Elm? That is pretty early, no?
Former Jarhead here- so same training and a lifelong shooter. I went there in 2003 and did the same thing, after years of reading about what an impossibly technical shot it was that trained marksmen couldn't replicate, etc etc.
I was surprised that, once standing in the window (next to it, actually) it was a lot easier a shot that I'd been led to believe.
I wouldn't be at all surprised if there was a lot of funny business surrounding the events of that day, which I won't render an opinion on, but the shot wasn't as tough as it seems often made out to be, IMO.
I am not going to try and get through your brainwashing. Anyone who cannot see that he was obviously hit from the rear and then the front is blind as a bat. Sorry....just is a fact.