Anatomy of a Headshot

This video was voted on by the sponsors of Questions for Science. You know what happens when someone gets shot in the head. "You get what you deserve!" They die. On the surface, yes: a

headshot

is a fatal wound, but beneath the gory reality, a lot happens when a bullet enters someone's skull. First things first, in terms of firearms, we're strictly talking about handguns and rifles, not shotguns, because a

headshot

is pretty self-explanatory. Let's start with the firearm, shall we? When a bullet is fired from a pistol or rifle, the bullet travels through a rifled barrel. A rifled barrel has grooves that cause the bullet to rotate.

When this rotating bullet penetrates the skull, its rotating motion flings cranial tissue outward. The tissue then expands to about 12 and a half times the diameter of the bullet, but only detensions for about 5 to 10 milliseconds and then contracts back to its normal size. For example, a .22 caliber bullet produces a 2.7 inch wound. A .38 caliber bullet creates a wound 4.4 inches wide and a .45 caliber bullet creates a wound five inches wide. Although very short, the expanded cavity causes a noticeable amount of damage to the skull. This wound creates a vacuum effect, causing air to rush in, causing the cranial cavity to expand and causing secondary fracture lines to extend from the wound.

Most fractures occur in soft places such as the temples and the orbital plates behind the eyes. The greater the power of the firearm, the more secondary fractures will occur in the skull, especially in the thicker and harder areas, such as the front and back. Speaking of high power, what factor do you think contributes to a bullet being more harmful to the human body? Its length, its speed or its weight? The answer is speed. To understand why, let's look at this kinetic energy equation. In this case, the kinetic energy of a bullet is equal to the weight of the bullet multiplied by its velocity squared, divided by the gravitational acceleration constant multiplied by two.

This may seem like a lot, especially if you haven't studied physics, but let me make it insultingly simple. More kinetic energy equals more ouch. The higher the kinetic energy of a bullet, the more damage it causes. And we can demonstrate mathematically how velocity does this. So let's make everything have a value of 10. Okay, so the weight is 10, the velocity is 10, and the gravitational constant is also 10. We run the equation and the kinetic energy is 50. Okay, great. When we double the weight of the bullet, the kinetic energy also doubles to 100. Now, if we double the velocity, the kinetic energy doesn't double, it quadruples.

When there is more kinetic energy, there is generally more damage. We're talking about a stronger pressure wave through the skull, more external gases entering the head, more secondary fractures and even splitting of the skull itself. That is why rifles are more lethal than pistols, not because of the weight, but because of the speed of the projectile. Now, let's see what happens inside the skull. When the bullet pierces the skull, it creates an entry wound approximately the size of the bullet. If it exits the skull, it creates an exit wound many times larger than the bullet itself.

This happens in almost every medium a bullet passes through, whether plastic, metal, wood, or bone. This is because as the bullet passes through the medium, it creates a shock wave in front of it, which widens. Additionally, the bullet may rupture or mushroom, increasing its surface area. As for the inside of the skull, the bullet causes the bone to bevel. The best way I can illustrate this beveling process is with a piece of Swiss cheese. This side of the cheese is where the bullet enters, and it is very clean and small. This side is where the bullet comes out and is very wide and flared.

This flare fragments pieces of the skull and launches them into the brain, causing further damage. Once in the brain, three things can happen to the bullet. One, you can brake and stop. If it loses enough energy when it pierces the skull, it will stop in its tracks inside the brain, probably at the other end of the skull. Two, it passes cleanly, or three, it bounces inside the head. Of the three, the least common is the third, which accounts for about 20% of all bullet trajectories. If the bullet was fired from a high-powered rifle, it will most likely pass.

If fired from a gun, it is likely to stop in the brain or ricochet. Also, an interesting fact: most skull ricochets are not like this, or the bullet bounces at an angle, although it happens, but not often. In most ricochets, the bullet follows the round groove of the skull. In reality, the skull is very strong and the bullet, having lost so much energy passing through it, simply slides along the groove, sometimes settling just below the scalp. Finally, what happens to the brain in this whole ordeal? Well, it's bad. The brain is a solid, inelastic and incredibly soft organ.

Unfortunately, these properties do nothing to reduce the damage the brain receives from a gunshot. In contrast, elastic organs such as the intestines, stomach and bladder receive less damage from gunshots. The energy of the pressure wave is dissipated because the tissue stretches. However, inelastic solid organs such as the liver, pancreas, kidneys, heart, and brain receive total damage from the pressure wave because the tissue does not stretch. Finally, the distance the bullet travels from the barrel to the head can also determine how damaged the brain is. If the shot is far enough, the bullet can ricochet off the head.

It will still cause an injury similar to a blow to the head with a baseball bat or hammer, but again, it won't actually penetrate the skull, but it will still cause serious damage. Of course, these shots are fired from over 100 yards away and come from low-powered firearms like a pistol or a .22 caliber. Contact shooting, on the other hand, in which the barrel of the firearm is placed on the victim's head and then fired, turns the brain into a literal pulp. This happens for two reasons: first, the bullet has the highest velocity when it hits the skull, releasing the most energy possible.

Do you remember this equation? Second, the hot, expansive gases behind the bullet follow it to the wound. These gases then expand in the victim's brain, turning it to pulp and, in some cases, causing the skull to split open. All that being said, believe it or not, headshots are not 100% fatal. On average, they are 90% fatal, given the right circumstances. In my next video, I will discuss how and why some people managed to survive being shot in the head and still live to tell the story. Also, recently, a lot of you have been asking me what my experience and work in immunodiagnostics is, which is really fun.

But being a scientist and just reading research articles is sometimes not enough research for my videos, especially when I talk about medical procedures, and I work in a totally different field. Um, that's where my dad comes in. He is a retired ICU nurse of 37 years and has seen a lot. He has been a great help to me, especially in some of my medical videos that address real, specific concepts and cases. I'd be lying if I said I did all the research myself, so this is a shout out to my dad for all the help he gave me on my channel.

Thanks Dad.