Shotgun exit wounds

"Unlike exit wounds created by rifled weapons, shotguns do not generally give rise to exit wounds unless there is a contact wound to the head, for example (where the exit wound is actually a reflection of the explosive effect of the gases expanding in the enclosed cranial vault), or where there is a 'through-and-through' wound to a limb at close range. Head wounds demonstrate ragged and irregular exit defects due to fragmentation of cranial contents with everted edges.

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Where the body is struck at increasing range, the shotgun pellets do not have enough energy to traverse the body, and particularly they do not have the energy to pierce the skin at the exit site, and it is not uncommon to find pellets lodged just under the skin at the back of a victim.

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Shotguns rarely produce an exit wound when fired into the chest or abdomen, though they often exit when fired at close range or a contact shot into the head, neck or mouth. The exit wound is large and irregular. The skull may explode open with all the gases inside, ejecting part or even all of the brain from the cranial cavity."

Various sources