>>516643847
That's his stealth armor vest at the back reacting to the bullet hitting the front armor. Note his rear skull react to the internal bullet hitting it from the inside after being deflected up from the armor.
The bullet came to rest in his cranial cavity.

>>516614909
This.
And there is no exit wound because the bullet lost a lot of energy after hitting the armor and didn't have enough power to burst through the back of his skull. The bits of bullet are still inside his brain.

>>516554708
The bullet hit the stealth armor that his friend confirmed he wears, deflected upward.