I get your point, but how do you shoot a person in the head from 10 feet with a .223 and have it fragment in their skull?
And nothing was mentioned about any other bullet impacts anywhere in the room.
Good thoughts, though.
I know virtually nothing about .223 bullets/ballistics.
Normally, I would expect a .223 FMJ bullet to zip right through a human head at that distance.
David Petraeus once took a 5.56 round through the chest and was up jogging two days later.
It could possibly be a manufacturing defect in the bullet itself.
There’s an electronic copy of Unintended Consequences at https://www.freedomsphoenix.com/Uploads/129/Media/Unintended_Consequences.pdf
Look at page 704, and you’ll find a reference to a bullet exploding in flight without hitting anything. In that case, the bullet is moving faster and rotating faster than the .223 bullet likely was, but it’s a possibility you might want to pursue.
You might also want to inquire over at www.ar15.com.