Staff Sergeant Nick Lavery wasn’t only the most physically imposing Green Beret on our team, he was the most physically imposing soldier any of us had ever seen. He was 6′5″, approaching 280 pounds, and cut like a linebacker—the position at which he excelled, not coincidentally, as a college football player at the University of Massachusetts Lowell. He was a weapons specialist, and an expert in hand-to-hand combatives. If Army scientists and tattoo artists had highjacked a Darpa lab to create the ultimate soldier, they would have created Nick. But that wouldn’t prevent a single gunshot to the leg from nearly killing him.

Most of what we learn about gunshot wounds, we learn from watching television. A small sliver of this programming is actually educational, like the ballistics tests performed on Mythbusters. (Some lessons: Bullets fired into liquids will stop or disintegrate rather than slice through seawater à la Saving Private Ryan, and a weapon that would blow a victim backwards would also blow the shooter back.) But these examples are outliers. Depictions of gun violence in fictional shows and movies are routine, and often wildly imaginative. Those depictions are distorting understanding of what bullets can—or can’t—do to bodies.

As a combat medic in Afghanistan, I treated a variety of gunshot wounds. And as the husband of an emergency room provider at Johns Hopkins Hospital in Baltimore, gun violence has remained—at least peripherally—a significant part of my life. This year, murder rates in Baltimore are on track to surpass death tolls generated by the crack epidemic. Through conversations I’ve had with ER doctors at Johns Hopkins, in addition to my own combat experience, I can offer a few tips you won’t learn at the movie theater. This isn’t just about exposing Hollywood sophistry: It’s about knowing what to do if you ever find yourself near or among the 297 or so people in America who are shot each day in homicides, assaults, suicides, suicide attempts, accidental shootings, and police interventions.

Lavery sustained his wounds at close range, the fateful round fired from a Soviet-designed PKM 7.62 mm machine gun. Lavery had quickly positioned himself between the shooter and a younger American infantryman, an instinctive decision for which he would receive the Silver Star. “I have no doubt that he saved my life," the infantryman said later in a sworn statement. Nick seemed indestructible. Earlier, during the same deployment, a grazing round scarred his face, and shrapnel from an exploding RPG injured his shoulder. On this day, his "good luck" ran out.

The femoral artery runs down the thigh, using the femur as a backstop. It supplies oxygenated blood to the leg, and in healthy adults is between 5 and 10 mm in diameter. The relatively small but powerful projectile that hit Lavery's massive leg barely could have followed a deadlier trajectory: It struck and shattered his femur, severing his femoral artery in the process. Unaware of the arterial damage, his powerful heart continued pumping large quantities of blood toward the oxygen-starved muscles in his right leg, causing valuable blood cells to accumulate uselessly in the expanding interstitial space. Without immediate medical intervention, the wound would have killed him. He survived, but lost his leg above the knee.

The threat of blood loss is not unique to Lavery: It’s the number one preventable cause of death on the battlefield. Ruptures to the body’s arterial thoroughfares—including brachial arteries in each arm, bilateral inguinal arteries in the groin, and the thick subclavian arteries sitting unnoticed beneath each clavicle—can potentially result in massive hemorrhaging. It isn’t uncommon to see heroes on the silver screen fighting courageously through their extremity wounds, when in fact the disruption of peripheral or junctional arteries can cause irreparable harm within minutes.

The human body does possess certain defense mechanisms in the event of rapid blood loss. The vascular system will “shunt” blood from the extremities into the core to maintain perfusion to vital organs, but that’s really only effective once the hole gets plugged. Sudden amputations, in particular, will cause the surrounding musculature to tense and contract. A complete amputation doesn’t look like the busted fire hydrants in Kill Bill—instead, it may take minutes or hours before they bleed heavily. Combat medics in training are reminded repeatedly of failures by their predecessors to properly identify and treat “clean” amputations, injuries that resulted in delayed but sudden exsanguination en route to a higher echelon of care.

Penetrating trauma and tissue damage from projectiles are a bit different. They have the potential to cut through arteries and large veins without alerting the body’s muscles to problems. With bullets, it all comes down to shot placement and passage—which, without the gift of surgical precision that no gunman will ever have, is another way of saying it comes down to luck. Aiming for limbs to create “flesh wounds” is a movie myth, and generally not something that police or soldiers ever train to do.

Furthermore, even multiple gunshots to the torso won’t guarantee death, or even incapacitation. Arun Nair is an attending physician in the ER at Johns Hopkins, and an International Health Fellow. “Bullets are magic,” Nair tells his students. He recounts the story of a young man in Lebanon who survived after being shot six times.1 He took repeated shots to the chest and throat. One of the six bullets stopped inside his pericardium, the narrow space between the heart and its thin protective membrane. Another bullet ended up in the victim’s esophagus; he swallowed it. Amazingly, the patient was alert and speaking lucidly to the doctors. You can't assume anything, says Nair. Bullets can bounce, ricochet, and change vector under the skin.

So, what can bystanders do when confronted with gun violence? First, if possible, stop the bleeding. Swelling and discoloration are signs of hemorrhaging anyone can recognize. Researchers studying American war zones have attributed 90 percent of preventable deaths to uncontrolled bleeding, and ordinary soldiers aren’t exclusively capable of managing blood loss. You can control hemorrhaging by applying manual pressure, or by fastening a tourniquet—improvised or commercial—high and tight on the limb.

What else is there to do? The answer is ... not much. A small percentage of combat deaths are due to a condition known as a “tension pneumothorax”—colloquially, a collapsed lung. The lungs have no muscles. They expand due to negative pressure inside of the pleural cavity, which means any type of hole is bad. The goal is to prevent any air from being sucked into the chest cavity, often with the application of an occlusive dressing, whether it’s tape, plastic, or an actual chest seal. Any hole between the neck and the navel is a potential concern. Identifying and treating the tension pneumothorax also is possible on-scene, but it requires training and equipment.

In a medical emergency, time is always critical, and obviously every effort should be made to evacuate casualties to a hospital. But survival may depend upon the quick instincts of a first responder. Is a gunshot wound to the chest preferable to one in the leg? Absolutely not. But doctors don’t take anything for granted, and neither should you.

Connor Narciso is a former Army Green Beret who served in Wardak Province, Afghanistan, with 3rd Special Forces Group.

1 UPDATE 14:20 12/08/15: This story has been updated to correct the location where the doctor treated his patient.

You may also like: