Does this look like an Exit Hole?
The answer is, no it does not. Having been a Small Arms instructor who has been around countless rounds down range with a 5.56 mm round from M16's, M4's, and the M249 SAW, and as the owner of AR15's myself, I can categorically state:
That looks exactly how metal looks when its been fired into with that type of ammo. There is a mushroom effect.
Lanza used S&B 5.56x45. (Sellier & Bellott)
On my "To Do" list for awhile is to find a piece of similar aluminum scrap and get the exact S&B ammo used by Animal Lanza and do a "Debunk" video. Since I was asked tonight, I decided to simply show a piece of scrap that I have on hand that has been hit by a 5.56 round fired from an AR15.
While it's not the same Ammo, this is very similar Ammo. While its not the same metal, it is similar in that it will demonstrate that "mushroom effect" that occurs on both entrance and exit of metal when hit with the rounds.
Also, its important to note that Animal was firing from near the restroom area of Room 10 and, thus at an angle. So in a recreation, that would have to be similarly recreated as well.
At any rate, there are some photos of a piece of metal fired into with an AR15 (same 1:9 twist) with similar ammo. This metal clearly shows that entrance and exit have almost identical mushrooming. A thorough debunking will come soon, but I just wanted a quick demonstration of effect on metal.
The window shots are perfectly normal for entrance holes. Anyone who tells you different, has never fire through metal thicker than an aluminum can.
This graphic depicts about where Animal was standing when he fired the rounds through the window. Note the angle
See also Part II:
Edited: Video created demonstrating the effect of an AR-15 round on aluminum