Great question Robert! This is a vast and confusing topic, with many key facts still open to debate. I’ll try to set down some helpful guidelines for the crime or fiction writer, to help you make your stories realistic. Here are some tips:

Distance from the shooter: Contact wounds will show soot and skin lacerations, close wounds will have soot, but not the lacerations, distant wounds create only a hole.

Penetration: A bullet must maintain a velocity of 200 fps to penetrate human tissue. Variables are firing distance, length and diameter of the gun barrel, kind of gunpowder, angle to the target, cartridge construction, caliber, wind, heat, rain, clothing, deflection (as off bone), and density of the tissue (as in lung vs. muscle). Most bullets are made to deform, remain in the body, and do not produce an exit wound. Full metal jacket and rifle bullets (traveling at over 2,000 fps) resist deformation and often produce an exit wound.

Determining direction from forensics: Bone will “cone” away from the line of fire. Two points of penetration inside the body may determine a trajectory. Multiple shots from the same shooter may have different trajectories within the body because the victim is moving (as in falling down). X-ray, CT, and MRI scans may be helpful to reconstruct bullet trajectories and recover bullet fragments in victims both living and dead.

Damage created: A bullet has 3 initial chances to cause damage. First is the main tract, limited to a narrow area. Second is the pressure wave that is created along the main tract and damages a wider area. Third, bullet fragments that break off and go their own way will create additional tracts and more damage. Soft bullets designed to minimize collateral damage may actually make a victim’s injuries worse. A shot to the head kills instantly 75% of the time. The heart and major blood vessels can burst from a direct hit, also causing instant death. Bleeding and lung damage may cause delayed death minutes later.

Shotguns: Beyond 5 yards, multiple projectiles from a shotgun will spread out and act independently. Tough clothing can slow down individual pellets. Pellets that do penetrate skin leave an entrance wound the same size as the pellet. Slugs will deform, leave a large entry wound, and proportional damage.

Suicide by gun: I thought to mention this, as it’s a common theme in mystery and crime stories, and must be ruled out in many police procedurals. About 70% of these suicides are done with a handgun, and 30% with rifles and shotguns. The right temple is the usual handgun target, while most who kill themselves with a rifle or shotgun prefer the mouth. About 97% of gun suicides will show the classic signs of a contact wound as I described above.

I recall being at a lecture on improving gunshot wound survival at a Northeast conference, and during Q&A, a Texas MD said, “We don’t have a gunshot wound survival problem in Texas. We use big caliber and kill ‘em where they stand!” The moral is, to keep your fiction realistic and storyline simple, just give your shooter a very big gun.

H.S. Clark, MD