A bullet enters the body in a relatively stable, nose-forward orientation and leaves after being destabilized by its passage through tissue, bone, and fluid. That destabilization, along with deformation and sometimes fragmentation of the projectile itself, is the main reason exit wounds tend to be larger and more irregular than entrance wounds. The difference is not simply about speed or force at the moment of exit; it reflects a chain of physical events that unfolds over the few milliseconds the bullet spends inside the body.
How a Bullet Changes During Its Path Through Tissue
When a bullet strikes skin, it is typically spinning and traveling point-first, punching a relatively neat hole roughly its own diameter. Once inside soft tissue, things change quickly. The bullet encounters far more resistance than air, and this resistance does not push evenly on all surfaces of the projectile. The bullet begins to yaw, meaning its nose tilts away from its direction of travel. In many cases it tumbles end-over-end. A bullet presenting its full profile sideways to tissue displaces far more material than one traveling nose-first, and by the time it reaches the exit site, it may be traveling base-first or at a steep angle. That enlarged, unstable cross-section tears a larger hole on the way out.
Deformation compounds the problem. Many bullet designs, particularly hollow-point and soft-point rounds, are engineered to mushroom open on impact. A jacketed hollow-point that enters at roughly its original caliber diameter can expand to nearly double that width as it passes through muscle tissue.1PubMed. The ballistic wounding capacity of the 22 Winchester Magnum projectile in the near human porcine tissue model Even full metal jacket rounds, designed to resist deformation, can distort or fragment when they strike dense structures like bone. The bullet that exits is often a physically different object from the one that entered.
Temporary Cavitation and the Pressure Wave
Beyond the permanent hole a bullet carves, there is a brief but violent expansion of the surrounding tissue called temporary cavitation. As the bullet passes through, it pushes tissue radially outward at high speed, creating a cavity many times larger than the bullet itself. This cavity collapses almost immediately, but the rapid stretch can tear blood vessels, damage organs, and weaken tissue along the wound track. In rifle injuries, where velocities are much higher, the temporary cavity can be dramatic, and the zone of damaged tissue surrounding the main wound track extends well beyond what the bullet physically touched.2PubMed. Wound ballistics 101: the mechanisms of soft tissue wounding by bullets
The temporary cavity tends to be largest at or near the point where the bullet has become most unstable, which is often closer to the exit side of the body. By that point, the bullet may be tumbling, expanded, or fragmenting, and it is sweeping through tissue with a much larger effective cross-section. The tissue at the exit site is being pushed outward not just by the bullet itself but by the pressure wave radiating ahead of and around it. This is a significant contributor to the ragged, blown-out appearance that exit wounds can have.
What Happens When Bullets Hit Bone
Bone changes the equation substantially. When a bullet strikes bone, several things can happen at once: the bullet may fragment, the bone shatters, and those bone fragments become secondary projectiles that radiate outward through surrounding tissue. A study examining different military rifle rounds found that SS109 bullets caused bone to fragment and the bullet itself broke apart, creating a shrapnel-like effect with large, irregular exit wounds. Heavier M80 rounds caused even more extensive tissue disruption due to their higher kinetic energy, producing wide, irregular exits.3PubMed Central. Experimental wounding models of different bullet types and diameters on extremities
Research specifically on skull wounds confirms that exit wounds in bone are almost always larger than entrances. In one study comparing entry and exit holes in skulls, exits were larger in all but a single case. The authors attributed this to the bullet’s deformation and instability after penetrating the initial layer of bone, even though the projectile has lost velocity by that point.4PubMed. Gunshot wounds to the skull: comparison of entries and exits This is an important detail: the bullet does not need to be moving faster at exit to make a bigger hole. Its changed shape and orientation more than compensate for the lost speed.
Hollow-point bullets that perform well in soft tissue may behave very differently in bone. Testing in porcine models showed that a jacketed hollow-point round expanded predictably in muscle but fragmented completely when it hit bone.1PubMed. The ballistic wounding capacity of the 22 Winchester Magnum projectile in the near human porcine tissue model Complete fragmentation sends dozens of small metal pieces through tissue in different directions, which can produce an exit area that looks less like a single wound and more like a cluster of perforations.
Handguns Versus Rifles
The size difference between entrance and exit grows considerably with bullet velocity. A multicenter study comparing wounds from high-velocity rifle rounds to those from conventional handguns found that the dimensions of exit wounds were significantly larger in the rifle group.5PubMed. The wounding potential of assault rifles: analysis of the dimensions of entrance and exit wounds and comparison with conventional handguns The ratio of exit-to-entrance size was also much higher for rifle wounds, meaning the disparity was not just about the wounds being bigger overall but about exits growing disproportionately relative to entries.
This makes intuitive sense when you consider the physics. Rifle bullets typically travel two to three times faster than handgun bullets, and kinetic energy scales with the square of velocity. That extra energy has to go somewhere as the bullet decelerates through tissue. Research on full metal jacket bullets passing through gelatin targets confirmed that higher impact velocities produce greater energy loss within the target medium, with the relationship between bullet path length and energy transfer being remarkably linear up to about 12 centimeters of penetration.6PubMed. The deceleration of full metal jacket bullets in compact target models – A new approach More energy deposited in tissue means more disruption, more temporary cavitation, and a more dramatic exit.
Handgun wounds, by contrast, often show a much smaller difference between entrance and exit. Low-velocity pistol rounds may pass through without significant yaw or deformation, especially if they do not encounter bone. In those cases, the exit wound can be only slightly larger than the entrance, and occasionally the two are similar in size. The general rule that exits are bigger still holds in most handgun cases, but the effect is far less pronounced than with rifles.
How Skin Properties Affect Wound Appearance
Skin is not a uniform material. Its thickness, elasticity, and fiber density vary across the body, and those differences affect what a wound looks like. Research measuring bullet entrance holes on different parts of the trunk found that wounds on the back, where the dermis is thicker and richer in connective tissue fibers, were considerably smaller than wounds in the same caliber on the front of the torso, where skin is thinner.7International Journal of Legal Medicine. Differing sizes of bullet entrance holes in skin of the anterior and posterior trunk The elastic properties of skin are strongly determined by its connective tissue, so the same bullet can leave different-sized marks depending on where it hits.
This has real implications for understanding exit wounds. Because the skin at the exit site is being pushed outward from the inside, the bullet must stretch and tear the skin to escape. Thicker, more elastic skin may resist that tearing better, producing a slightly smaller or more slit-like exit wound than you might expect from the damage visible internally. Thinner skin, or skin over areas with less subcutaneous support, tears more readily and can produce exits that appear disproportionately large relative to the internal wound track. The body region where the bullet exits matters almost as much as the bullet itself.
When Exit Wounds Look Smaller Than Expected
Not every exit wound is dramatically larger than its corresponding entrance. There are several scenarios where the expected pattern breaks down, and forensic pathologists have to account for all of them.
The most well-documented exception is the shored exit wound. This occurs when the skin at the point of exit is pressed against a hard surface at the moment the bullet emerges. If someone is lying on concrete, leaning against a wall, or wearing a rigid belt buckle over the exit site, the outgoing bullet sandwiches the skin between itself and that unyielding surface. The result is an abraded ring around the exit wound that mimics the abrasion collar typically seen around entrance wounds.8PubMed. Shored gunshot wound of exit. A phenomenon with identity crisis The supporting surface essentially “shores up” the skin, preventing it from tearing open as widely as it otherwise would and leaving behind a wound that can fool an untrained observer into thinking it is an entrance.
Shored exit wounds have caused confusion in forensic investigations for exactly this reason. They combine features of both entrance and exit wounds, and different surfaces produce different abrasion patterns. Research testing a range of forensically common surfaces confirmed that the presence of any rigid backing at the exit site reliably produces an abraded ring, though the specific morphology varies with the surface material.9PubMed. An investigation of shored gunshot exit wound morphologies using a range of forensically relevant surfaces Experienced pathologists look for a scalloped or irregular pattern within the abrasion collar, along with the radiating skin lacerations characteristic of exits, to distinguish a shored exit from a true entrance.8PubMed. Shored gunshot wound of exit. A phenomenon with identity crisis
Other situations can also produce misleadingly small exits. A bullet that has lost most of its energy, particularly one at the extreme end of its effective range or one that has already passed through an intermediate barrier, may exit with barely enough velocity to break through the skin. In those cases the exit wound can be a small, irregular slit rather than a gaping hole. Similarly, certain bullet types that stay intact and do not deform significantly, like some full metal jacket rounds fired from handguns, can exit without the dramatic size increase people expect from movies.
How Forensic Pathologists Tell Entrance from Exit
Given that exit wounds are not always obviously larger, forensic examiners rely on a constellation of features rather than size alone. Entrance wounds typically have an abrasion collar, a ring of abraded skin caused by the bullet scraping inward. They may also show soot deposition or stippling from unburned gunpowder if the shot was fired at close range. The edges of an entrance wound tend to be inverted, meaning the skin is pushed inward along the wound margin.
Exit wounds generally have everted or outward-turned edges, with irregular or stellate (star-shaped) tearing. They lack soot and stippling because those are products of the muzzle blast, which only affects the entrance side. In bone, the distinction is often even clearer: entrance holes in the skull typically show beveling on the inner table of bone (the side the bullet is traveling toward), while exit holes show beveling on the outer table. The skull study mentioned earlier confirmed that these bone-beveling patterns, combined with size, are highly reliable for determining direction of travel.4PubMed. Gunshot wounds to the skull: comparison of entries and exits
No single feature is considered definitive in isolation. Shored exits can mimic abrasion collars, contact entrance wounds can produce stellate tears that look like exits, and atypical bullet behavior can blur the lines. Pathologists use the full picture: wound morphology, internal wound track direction, presence or absence of soot, bone beveling, and the physical evidence at the scene.
Why Ballistic Research Is Harder Than It Looks
Much of what we know about wound ballistics comes from testing in tissue simulants, most commonly ballistic gelatin calibrated to approximate the density and resistance of human soft tissue. But a systematic review of gelatin-based ballistic research found significant problems with comparability across studies. Differences in gelatin concentration, temperature, mold shape, and aging all produced meaningful variation in how bullets behaved, including changes in penetration depth, yaw angle, and temporary cavity size.10PubMed. Ballistic gelatin as a soft tissue simulant: A systematic review of applications, calibration methods, and synthetic alternatives Few studies even reported basic calibration checks, making it difficult to compare results from different labs.
Synthetic alternatives to gelatin, made from materials like SEBS elastomers, have gained popularity because they are easier to handle, reusable, and transparent, which allows high-speed photography of the wound channel. But these synthetics come with their own limitations. They tend to increase penetration depth and delay the onset of yaw compared to gelatin, which means they may underestimate the wounding effects that occur in actual tissue at a given distance.10PubMed. Ballistic gelatin as a soft tissue simulant: A systematic review of applications, calibration methods, and synthetic alternatives Neither gelatin nor synthetics perfectly replicate the layered structure of real anatomy, with its combination of skin, fat, muscle, fascia, organs, and bone at varying distances. The field has been working on these problems since the nineteenth century, when early researchers first connected bullet deformation and energy transfer to tissue disruption.11Forensic Science, Medicine and Pathology. Historical overview of wound ballistics research Despite enormous progress, the exact mechanisms behind remote tissue damage from high-energy projectiles remain an active area of investigation.
Energy Transfer Is Not the Whole Story
A common simplification holds that bullet damage is purely a function of how much kinetic energy the projectile dumps into tissue. There is truth to this: higher impact velocities do correlate with greater energy loss in the target, and more energy deposited generally means more tissue disruption.6PubMed. The deceleration of full metal jacket bullets in compact target models – A new approach But energy alone does not explain wound patterns. Two bullets carrying identical kinetic energy can produce vastly different wounds depending on their construction, how they deform, whether they fragment, and what tissues they encounter.
A full metal jacket round that passes cleanly through soft tissue without hitting bone may deposit relatively little energy and exit with a wound only modestly larger than its entrance. A hollow-point round at the same velocity that mushrooms open in muscle dumps far more energy into a smaller volume of tissue, potentially producing a devastating exit wound or, if the bullet expands enough to slow below exit velocity, no exit wound at all. A fragmenting round scatters its energy across multiple wound tracks, each with its own exit potential. The physical state of the bullet at the moment it reaches the exit site, its shape, orientation, number of pieces, and remaining velocity, matters at least as much as its initial energy.
This is why sweeping generalizations about exit wounds can mislead. The “classic” exit wound, a large, ragged, blown-out hole, is most consistently seen with high-velocity rifle rounds or expanding ammunition that strikes tissue with enough energy to deform and still exit. Plenty of real-world gunshot wounds do not match that textbook picture, and forensic professionals spend careers learning to read the specific combination of factors that produced each individual wound.