Here is the problem with the 911 conspiracy theory's......

[zeemike]

116. No sir the shutter speed is all that is relevant.

Because what is on the frame is due to how long the frame is exposed to light...the shutter speed determines that.
And so the bullet must have struck before the shutter opened in order to effect the head movement...and quite a bit before because of inertia the head does not move instantly when struck.
So that leaves you with the problem of fitting the time line of the bullet taking so long to traverse the skull.
But the whole body did not move...it was seated and could not....but the head has much less mass than the whole body and wold move if a high velocity bullet struck it...and that is not a theory but a fact of physics....especially with an exploding bullet where the entire force of the bullet is dissipated on the head.
And those several frames of back head snap is consistent with a shot from the front...Inertia is the explanation of why it last for several frames because the force is transferred instantly but inertia tends to hold the head at rest....all calculable by the way sense we know the mass and speed of the bullet and the mass of the head.
But don't look to me to do the math for you ....I don't need to prove you wrong...you need to prove you right.

And BTW...the particles ejected buy the bullet if it came from the back or front would have little mas and so would have little resistance to the force of inertia...probably not even measurable really...and so at 2500fps it would be about 1/600 of a second to move 4 feet...but maybe if it went through the skull it slowed way down to 500fps...that means it would have been only 1/100 of a second...
Sorry but you still got big problems with making ift fit in time.