The Final Truth: Solving the Mystery of the JFK Assassination also demonstrates that Oswald’s carbine was not sticking out of the window but remained entirely inside (p. 45).  The muzzle was stabilized on the far edge of the box resting on the windowsill.  This frame from the Secret Service film also shows that Oswald, in setting up the boxes for support, had planned from the outset to fire as the target was moving away on Elm Street, positioning himself to minimize the apparent movement of the target.

 

 

The Final Truth: Solving the Mystery of the JFK Assassination
Paperback: http://www.amazon.com/gp/product/1490350578
Kindle: http://www.amazon.com/dp/B00CPSBM7U