Clinical ballistics: pistol, rifle and shotgun effects

The following scene is fictional and was written for teaching. It is two in the morning and two casualties arrive from the same shooting. The first has a small hole in the thigh, almost no bleeding, and is talking normally. The second was hit in the abdomen by a long gun and is pale, cold and confused. The resident remarks that the first "looks simple" and the second "looks serious". Both impressions may be right, but for reasons different from the ones she imagines. The size of the entry hole says little. What defines the injury is how much energy the projectile delivered to the tissue, where it passed and what it met along the way.

This text explains, based on reviews and experimental studies, what wound ballistics (the study of how a projectile behaves inside the body) really adds to clinical assessment. The idea is not to turn the clinician into an expert, but to give them a mental model that helps predict injuries, avoid traps and talk to the surgeon in the same language. The content is educational and does not replace local protocols or the assessment of those at the bedside.

Key points

• The severity of a gunshot wound depends on the energy transferred to the tissue, and not only on the velocity or the caliber of the projectile.
• Low-velocity weapons, such as most pistols, stay below about 600 m/s; rifles usually exceed that limit.
• The permanent cavity is the destroyed track; the temporary cavity stretches the surrounding tissue and damages less elastic organs more.
• Yaw, fragmentation and deformation of the projectile greatly increase the energy delivered.
• A shotgun has a lower muzzle velocity, but at short range it produces destruction comparable to that of high-energy weapons.
• Removing every projectile and debriding widely is usually unnecessary; the decision follows the injury, not the metal.

Why ballistics matters in the emergency room

Gunshot wounds are an important cause of hospital admission in many countries. In an analysis of the United States national inpatient database, there were on average 30,617 admissions per year for firearm injuries, and about 70 in every 100 injuries with a known weapon type were caused by handguns (Peek-Asa and colleagues, 2017). This means that most of what arrives at a civilian emergency department is produced by low-energy projectiles. At the same time, the clinician needs to recognize when they are facing something different: a rifle, a shotgun fired at close range or a projectile that fragmented.

The literature on civilian trauma insists on one point: knowing basic principles of ballistics helps anticipate the injury pattern and avoid decisions guided by the appearance of the skin (Lichte and colleagues, 2010). A small hole can hide a deep vascular injury. A large exit hole does not mean that every organ along the track was destroyed. The skin is elastic and often underestimates what happened beneath it.

There is also a practical reason. In a recent review focused on orthopedics, the authors recall that the way the projectile behaves influences debridement, antibiotic use, fracture stabilization and the decision whether or not to remove the metal (Baum and colleagues, 2022). Those who understand the mechanism tend to request fewer unnecessary procedures and to be more suspicious when the story does not add up.

Energy, velocity and mass: what each one explains

The kinetic energy of a projectile grows with mass and with the square of the velocity. That is why velocity usually receives more attention. Reviews of civilian trauma use a cutoff of about 600 m/s: below that are low-velocity weapons, such as most pistols and revolvers; above it, high-velocity ones, such as many rifles (Lichte and colleagues, 2010).

The problem is that the energy the projectile carries is not the same as the energy it delivers. A very fast projectile that passes straight through a limb, without tumbling or breaking up, can exit carrying much of the energy with it. A slower projectile that deforms and stays lodged delivers all its energy to the tissue. That is why wound ballistics texts speak of transferred energy, not available energy (Baum et al., 2022).

The factors that increase energy transfer are relatively stable across sources:

• Projectile yaw, that is, how much it tilts relative to the flight axis.
• Fragmentation, which multiplies the paths and the contact surfaces.
• Deformation or expansion of the tip, which increases the frontal area.
• Entry profile and firing distance.
• Density and elasticity of the tissue hit.
• Presence of barriers, such as thick clothing, glass or bone, which can destabilize the projectile.

This reasoning helps explain why two wounds from the same weapon can have opposite courses. The tissue changes, the path changes and the projectile's behavior changes with them.

Permanent cavity and temporary cavity

When a projectile passes through tissue, it produces two effects. The first is the permanent cavity, the tunnel of tissue crushed and destroyed by direct contact. The second is the temporary cavity, a rapid radial expansion that pushes tissue away from the path and then collapses in fractions of a second (Lichte et al., 2010).

In low-velocity weapons, the temporary cavity is small and the injury is almost confined to the path. In high-velocity ones, it can be much larger. A vascular imaging review describes that, with high-velocity weapons, the cavitation zone can reach 25 times the projectile caliber (Gopireddy et al., 2023). This explains vascular and nerve injuries away from the visible path.

The effect of the temporary cavity depends on the tissue. Muscle, lung and bowel loops are relatively elastic and tolerate stretching well. Liver, spleen, kidney and brain are poorly elastic and rupture. Bone can fracture even without direct contact. Therefore, the same projectile can leave a clean path in the thigh and an explosion of tissue in the liver.

Studies in ballistic gelatin help visualize these cavities, but they have limits. A review on the use of gelatin in wound ballistics notes that clothing, protective equipment and real tissues produce penetration depth and damage different from those observed in the block, which calls for caution when extrapolating laboratory images to the patient (Carr et al., 2018). In an experiment comparing porcine thorax with gelatin blocks, the .223 rifle projectile, which tends to expand on impact, had a penetration depth in the thorax different from that measured in gelatin at 20 per 100 concentration (Mabbott et al., 2016). Gelatin is a useful model, not a photograph of the body.

Yaw, fragmentation and deformation of the projectile

Rifle projectiles are long and have their center of mass closer to the base. In flight, they are stabilized by the rotation given by the barrel. On entering a dense medium, they lose this stability and tend to tumble, presenting their side to the tissue. When this happens, the contact area increases and the temporary cavity grows. A study in limbs from animal cadavers showed that projectiles destabilized before impact, as happens when passing through clothing or barriers, yaw earlier and produce wounds different from those obtained with targets without a barrier (Stevenson et al., 2020).

In the same study with porcine thorax and gelatin, the authors describe that the 9 mm Luger pistol projectile usually does not fragment, but tends to yaw inside the target, while the .223 Remington with an exposed tip usually expands on impact (Mabbott and colleagues, 2016). A study by the same group, also in animal cadaver limbs, assessed the effect of layers of military clothing and concluded that a minimal layer of clothing did not change the damage produced by 7.62 mm and 5.45 mm projectiles, which shows that not every barrier changes the outcome (Stevenson and colleagues, 2019). The practical result is that fragments can spread outside the main track and reach structures that the imaginary line between entry and exit did not suggest.

Hollow-point or soft-point projectiles were designed to deform. They open on entering tissue, increase the frontal area and tend to be retained, which maximizes the energy delivered. Fully jacketed projectiles, more common in military use, tend to keep their shape, but can yaw and break when they hit bone. In all cases, the radiograph shows the final result, not the path. A fragment stopped in the pelvis may have passed through the intestine, the bladder and a vessel before reaching there.

Pistol, rifle and shotgun side by side

The comparison between the three major groups of weapons summarizes what has been discussed so far. It should not be used as a rigid rule, because each ammunition has its particularities, but it helps organize the clinical suspicion.

Characteristic	Pistol or revolver	Rifle	Shotgun
Typical velocity	Below about 600 m/s	Above about 600 m/s	About 1,000 to 1,500 feet per second at the muzzle
Projectile	Single, short	Single, long and unstable in tissue	Multiple pellets or a single projectile (slug)
Temporary cavity	Small	Large, can reach dozens of times the caliber	Depends on distance
Injury pattern	Restricted to the track, except for fragmentation	Injury away from the track, comminuted fractures	Massive destruction at close range, multiple superficial injuries from afar
Foreign body	Projectile or fragments	Multiple fragments	Pellets, wad and clothing remnants

The shotgun data come from a review that recalls that, despite the relatively low muzzle velocity, a shotgun fired at close range produces a high-energy type of wound, because the entire load of lead hits the body as a single mass (Baum and colleagues, 2022). As distance increases, the pellets spread out, lose energy and start to produce multiple small injuries, with particular risk to the eyes.

In practice, the clinician rarely knows with certainty which weapon was used. The history is usually incomplete and sometimes false. Therefore, the injury pattern found on examination and imaging is more reliable than the account. Many fragments scattered on the radiograph suggest fragmentation or a shotgun. Extensive comminuted fracture with a small hole suggests high energy. A single intact projectile suggests low energy.

How tissues respond to energy

Each system reacts in its own way. In the skull, energy is transmitted to a brain that is not very elastic and is held in a rigid box, and even low-energy projectiles can cause devastating injuries. In the thorax, the lung tolerates stretching well, but the heart and great vessels do not forgive. In the abdomen, hollow viscera are relatively tolerant and solid ones rupture. In the limbs, the main concern is with arteries, nerves and bone.

A review on the physics of brain trauma proposes that perhaps the best way to define low and high velocity is by the nature of the injury: at low velocity, the damage stays localized along the track; at high velocity, the contribution of cavitation is added, and it does not accompany the low-velocity injury (Young and colleagues, 2015). This functional definition is useful in clinical practice, because what matters is the pattern found in the patient.

A practical summary of how each tissue usually behaves in the face of cavitation:

• Muscle and skin: elastic, they tolerate stretching well, but the skin can underestimate the deep injury.
• Lung: low density and high elasticity, it usually has injury restricted to the track.
• Bowel loops: relatively tolerant, but they can have multiple perforations and late wall injuries.
• Liver, spleen and kidney: not very elastic, they tend to fragment with wide cavitation.
• Brain: confined in a rigid box, it suffers greatly from small pressure variations.
• Bone: it can fracture in a comminuted pattern and produce secondary fragments that act as new projectiles.

Vascular injury deserves special attention. In a Swedish registry of 1,010 patients injured by firearms, 162 had vascular injury. The lower limb was the most common site, with 41.7 per 100 of these injuries, and the common femoral artery accounted for 17.6 per 100 (Nyberger and colleagues, 2023). These numbers help explain why any wound at the root of the thigh deserves careful vascular examination.

The same vascular imaging review notes that hollow organs and muscle tolerate cavitation better, while vessels can suffer intimal injury, thrombosis, pseudoaneurysm or arteriovenous fistula even without direct contact with the projectile (Gopireddy and colleagues, 2023). A palpable pulse therefore does not rule out arterial injury, and the examination must be repeated.

What ballistics change in the initial assessment

The initial approach to any person injured by a firearm follows the logic of trauma care: hemorrhage control, airway, breathing, circulation and neurological assessment. The content on field hemorrhage control with a tourniquet and the MARCH sequence details the prehospital phase. Ballistics comes in afterwards, helping to interpret what is seen.

Some reasoning adjustments derived from ballistics:

• Count holes and projectiles. An odd number of holes without a corresponding projectile on imaging suggests a projectile lost in another region or embolized.
• Estimate the path without relying on it too much. Fragments and projectiles deflected by bone depart from a straight line.
• Examine the distance of the path. With high-energy weapons, nearby nerves and vessels may be injured without direct contact.
• Do not classify holes as entry or exit based only on size. That is a forensic task and is frequently wrong.
• Consider non-metallic foreign bodies. Clothing, shotgun wadding and glass do not show up well on plain radiography.

Ballistics also plays a role in infection prophylaxis. In a prospective study of 530 patients with low-energy extremity wounds, a single intravenous dose of a first-generation cephalosporin resulted in deep infection in 0.8 per 100 patients and infection of any type in 11.1 per 100 (Nguyen and colleagues, 2022). High-energy wounds, with extensive muscle destruction or gross contamination, follow a different logic and are usually treated as severe open fractures.

Myths that get in the way of reasoning

Some popular notions about firearms do not hold up against the literature and can lead to clinical errors. The first is the idea that the projectile becomes sterile because of the heat of the shot. Fragments of clothing and skin dragged into the path carry contamination, and infections do happen.

The second is the belief that every projectile must be removed. The review by Baum and colleagues notes that removal of the projectile and formal debridement are often unnecessary and can cause additional damage, infection, iatrogenic neurovascular injury, deep vein thrombosis and bleeding (Baum and colleagues, 2022). The same review observes that the risk of lead poisoning is uncommon, except when the projectile is in contact with synovial fluid or the intervertebral disc.

The third myth is that velocity is everything. Fast projectiles that pass through tissue without yawing can cause smaller injuries than slow projectiles that deform. The fourth is that the exit hole is always larger than the entry hole. This often fails, especially in contact shots, where the entry wound can be large and irregular because of the action of gases.

The last myth is that the image shows everything. CT helps a lot, but metal artifacts can hide injuries near the projectile. MRI, in turn, is usually avoided when there is metal of unknown composition. When in doubt, serial clinical examination remains a central tool, as discussed in the text on diagnostic uncertainty and strategies for deciding well.

Infection, antibiotics and what to do with the metal

Ballistics also helps explain why every gunshot wound is treated as contaminated. When it breaks through the skin and organs, the projectile can carry into the tissue microorganisms from the skin, clothing, the environment and the digestive or urinary tract itself when the path passes through them (Baum and colleagues, 2022). A level I trauma center cited in that review reported infection in up to 15.7 percent of wounds, and high-energy wounds seem to become infected more often, because they leave more devitalized tissue (Baum and colleagues, 2022).

This does not mean every wound needs extensive exploration. In the same review, the authors note that many clinicians still believe removing the projectile and debriding widely is indicated in all cases, although management depends on the tissue involved and the presentation. A 2022 survey cited by them showed that only 14.5 percent of the participating surgeons had an institutional policy for projectile removal (Baum and colleagues, 2022). The lack of a written rule leaves room for decisions guided by habit, not by the injury pattern.

The European review on civilian ballistic trauma follows the same line. In high-energy and shotgun wounds, debridement must be aggressive, with removal of clothing and wadding trapped along the path and scheduled re-explorations. Clearly healthy tissue, however, should not be removed, because several studies suggest that excessive debridement causes more disability than the projectile itself (Lichte and colleagues, 2010). In fractures from low-energy projectiles, treatment usually follows that of the equivalent closed fracture, and stabilization depends on bone stability, not on the fact that there is metal nearby (Lichte and colleagues, 2010).

In practice, the reasoning comes down to three questions: how much energy was transferred, which tissues were in the path and what was left inside the wound. The answers define the degree of cleaning, the need for further surgery and follow-up.

How NEXO helps train this reasoning

Training with fictional clinical cases helps recognize patterns before meeting them on shift, as long as each clue is read calmly and checked against the hypotheses that are still open. In a case of penetrating trauma, the clues may point to an injury pattern that only makes sense when you think about transferred energy, path and tissue. Reading the clues carefully, without closing the case too early, is the same exercise described in the text on a diagnostic pause before closing the case.

Those who want to go deeper into the method can read about how to train differential diagnosis with clues and about clinical decision-making. The text on blast trauma and injuries that do not appear right away complements this one, because explosive fragments follow similar principles. To learn about the points and rewards system, see the NEXO Economy page. There are also tracks for those who do research (Researcher), for those who review cases (Curator), for those who produce content (Creators) and for those who want to follow results (Closer).

Frequently asked questions

Does a larger caliber always mean a more severe injury?

Not necessarily. Caliber influences the permanent cavity, but severity depends above all on the energy transferred, which varies with velocity, yaw, fragmentation, deformation and the tissue hit. A small, fast projectile that fragments can cause more damage than a large, slow one.

Can you tell from the wound whether the weapon was high-velocity?

Sometimes there are clues, such as tissue destruction out of proportion to the hole, highly comminuted fractures and many fragments on imaging. But the skin underestimates the injury, and reliably identifying the weapon is a forensic task. In clinical practice, the injury pattern guides management.

Why is a close-range shotgun wound so destructive if the velocity is lower?

Because the entire load of lead hits the body concentrated, with a high total mass, and delivers almost all the energy to the tissue. As distance increases, the pellets spread out and each one carries little energy.

Does every retained projectile need to be removed?

No. Removal is usually reserved for specific situations, such as an intra-articular projectile, contact with cerebrospinal fluid, causing compression, infection, localized pain or signs of lead poisoning. The decision is individual.

Does ballistic gelatin reproduce the human body?

It is a standardized simulator and useful for comparing ammunition, but real tissue has skin, fascia, bone and organs with different elasticities. Comparative studies show differences in behavior, so gelatin results must be interpreted with care.

Take-home messages

• Think in terms of transferred energy, not just velocity or caliber.
• Remember that the temporary cavity damages less elastic organs more.
• Count holes and projectiles and look for what is missing.
• Question straight-line paths when there is bone or fragmentation.
• Examine nearby vessels and nerves, even without apparent direct contact.
• Treat a close-range shotgun wound as a high-energy injury.
• Decide on projectile removal based on the injury and the location, not on the presence of the metal.

If you like reasoning from clues, the case of the day is waiting on the NEXO home page.

References

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9. Stevenson T, Carr DJ, Gibb IE, et al. Preliminary effect of projectile yaw on extremity gunshot wounding in a cadaveric animal model: a serendipitous study. Int J Legal Med. 2020. PMID 32162008.
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