Good questions, I don't have answers. @Doc_Glock might be able to suggest demineralization of the bone from the X-ray. I can't.
That is a humerus hit with two 5.56 rounds. Both entered very close to the target, no intermediate targets and no bony injuries before they hit the humerus. I think everyone can see the difference. That's why I was wondering if that bullet is something that had a bit more ooomph to it.