One thing I still haven’t heard about is the type of rifle used. Early on the day of the shooting, it was called a .22. Later in the day it was called an AR style rifle.
still might not be the final answer...............
I read he bought 50 rounds that day. I don’t think 5.56 usually comes in a box of 50 but .22 does. Also, wouldn’t 5.56 at 150 yards pretty much shred/remove an ear?