If you read and understand every word of Oswald’s Marine Corps Score Book, you’ll realize he was a crack shot and very familiar with the nuances of marksmanship, including zeroing the windage and elevation screws even on the fly during Rapid Fire.  (It’s why his first shot at JFK ‘missed.’)   

The Final Truth: Solving the Mystery of the JFK Assassination

http://www.amazon.com/gp/product/1490350578