IF, and that is HUGE in the way of emperical evidence, there had been a shot to Zapruders right the camera would have giggled in such a fashoin as to make the head shot a complete blur. The proximity fo the shot IF from the grassy knoll would have been in FEET instead of the yards from the TSBD.
That is not the case. The frames showing the head shot are crisp, without residual distortion of blurring from the report until AFTER the sound fo the shot has reached Zapruder.
I have walked the length of Dealy Plaza on many occassions. It is a fishbowl. Especially along Elm from the TSBD.
The Zapruder film shows all three shots and the aftermath. Kennedy is in his back brace, which he wears because of the surgery he has had to repai part of a disc. It is a horrible contraption that does not allow for much movement. It is a contributing factor to his death.
1st shot. A clean miss. Possibly due to the scope being off from Oswald dumping the rifle after the Walker attempt. The first shot hits the street behind the motorcade sraying the occupants with gravel and shrapnel (the autopsy report shows shrapnel pieces in the outer skull area including a piece of the jacket.) and wounding James Tauge under the Triple overpass.
Oswald realizes the scope is not going to work. The scope itself is on a mount the goes over the action, but allows for iron sight usage.
2nd shot. Oswald concentrates on Kennedy's head and fires. He does not allow for 'lead' and the bullet strikes Kennedy just at the collar line. This is the 'magic bullt shot' We will get to this in a moment and most likely would have been fatal.
[335] “There is an undisplaced fracture of the proximal portion of the right transverse process of T1.” Quote from the report of the HSCA consulting radiologist, G.M. McDonnel, MD, in: HSCA vol.7: 219. 
3rd shot. Oswald does it right. The slope of Elm Street now has Kennedy almost moving away in a straight line at about 9 mph. The brace Kennedy is wearing is holding him almost straight up. The second shot has left him virtually paralyzed with damage to the spinal collum.
I have examined hundreds of Carcano rifles and carbines, including one just yesterday that was factory fresh with cosmoline still in the reciever. The action was as smooth as any rifle action. It would only take a few turns of the bolt to take any of the 'rough edges' of a military rifle out. There is ample evidence Oswald did just that.
The 6.5 Carcano cartridge is a high velocity(2296 fps muzzle velocity), lightweight cartridge. It has a heavy copper-nickle jacket according to Geneva Convention. It is meant for high penetration evidenced by the damage done to Kennedy and Connaly. The 'magic' bullet is anything BUT pristine. 