To enter the surface of a bone a bullet must be traveling a minimum of 200 ft./sec.  There are three main types of gunshot wounds: penetrating, perforating, or both.  A penetrating wound is one in which there is only an entrance wound (see first photo in fragments).   A perforating wound is one in which there is both an entrance and exit wound (see the fourth photo in entrance wounds).  It is also possible to have both if the bullet goes through the skull and brain before becoming lodged under the scalp; there is a penetrating wound of the head, but a perforating wound of the skull and brain (see the last photo in exit wounds).  This is the most common type of wound, but it is variant on the caliber of the bullet, whether it has a full-metal jack or a semi-metal one, the location of the entrance site, and the distance of the gun when fired.
 

ENTRANCE VERSUS EXIT WOUNDS:

Entrance wounds:

• On the skin, these wounds leave what is termed an abrasion ring - a reddish zone of abraded epidermis (see the last photo in burns).
• On the bone, these wounds cause an oval to circular shaped injury that has a punched out look to it.  These wounds also bevel in because bone bevels in the direction in which the bullet is traveling (see photos in entrance wounds).
• It is sometimes possible to determine the caliber of the bullet by measuring the diameter of the entrance wound.
• Entrance wounds are associated with a lot of fracturing.

• These wounds tend to be larger and more irregular than entrance wounds.  This is due primarily to two factors:
• The spin of a bullet is what stabilizes it and this spin is not as effective when the bullet is in tissue due to its density.  The bullet will eventually begin to tumble end over end.
• The bullet may also become deformed was it passes through the body thus causing the exit wound to be larger than the entrance wound.
• These wounds bevel out (see photos in exit wounds).
• They also have less fracture patterns than the entrance wounds do.
• Pseudo exit wounds are those in which the bullet enters the brain and strikes the other side with enough force to drive a piece of bone out, but the bullet itself does not exit.

These types of wounds are caused by bullets that strike the skull at a shallow angle and thus split the bone into two fragments.  Therefore, what appears to be one hole is actually the entrance and exit wounds combined.  Experts can tell the difference because one end will have sharp edges (entrance wound) while the other edge will have external beveling (exit wound).    In these cases, the bullet does not actually enter the cranium, but death can still occur because the fragment of bone from the entrance wound is commonly driven into the brain.
 

FRACTURE SEQUENCE:
 

Photo courtesy of Reichs, p. 346

PUPPE'S RULE:

Puppe's Rule states that if multiple gunshot or blunt force trauma wounds are present it is possible to establish the sequence of shots/hits.  A fracture will stop when it hits another fracture (fractures travel faster than bullets) because the energy has somewhere to go.  Therefore, if one fracture hits another one and then stops, the fracture where it stops must have come first.


Photos courtesy of Dirkmaat, Lab Methods


 
 
 
 
 
 

GUNSHOT FRACTURES VERSUS BLUNT FORCE FRACTURES:

Ballistic:

• rapid
• ft/sec (ex. 600-800 ft/sec)
• fractures:
• plug and spall
• radiating
• concentric heaving (due to pressure) - see secondary fracturing
• no delamination
• energy does not cross fractures (which are faster than bullets)

• slow
• mph
• fractures:
• radiating
• concentric (due to impact pushing in)
• plastic deformation (this keeps skull from easily being put back together - is like pulling a rubber band too far so that it does not go back to its original position)
• delamination (skull bones act in layers)

Image courtesy of Dirkmaat, Lab Methods



 
 

* Images courtesy of Dirkmaat, various pages