Most people don’t understand what a bullet does, but that’s not surprising. The science of how a bullet behaves — ballistics — is complicated. Here is a basic explanation that may not satisfy everyone, but it should be helpful to most people.

Internal ballistics apply to what happens inside the firearm’s chamber (where the cartridge is held) and in the barrel of the firearm. The volume of the case, the weight of the powder, the degree to which the powder fills that space, the burning rate of the powder, and the weight of the bullet all factor into what happens before the bullet exits the barrel. The average person needs only to know that it’s not magic. It’s physics.

External ballistics explain the flight of the bullet. From the instant the bullet exits the barrel, gravity and air resistance take over. If the barrel is horizontal to the ground, the bullet begins to drop. We compensate for that drop by angling the barrel slightly upward. The bullet’s path becomes an arc affected by the bullet’s velocity, shape, and weight.

Terminal ballistics describe what happens when the bullet hits the deer, and plenty of things affect this. It’s possible for a bullet to zip through the deer without doing much damage, but that’s rare. Even if the bullet hits what hunters call “the boiler room” (the heart/lung area), that doesn’t mean every deer dies the same way or at the same speed.

Terminal ballistics begin with the bullet’s impact and continue with penetration. It matters where the deer is hit, but the weight, design, and velocity of the bullet also matter. A hollow point, a soft point, and a fully jacketed bullet will have different effects. The thickness of the copper jacket is also a factor. A hunting bullet is designed to expand, losing its original shape as it plows through the deer’s tissue. “Mushroom” is the word used to describe bullet expansion.

Ideally, the bullet retains its weight, although that never actually happens with a lead-core, copper-jacketed bullet. The jacket peels back and the lead becomes more exposed. Lead is soft, so it loses mass. Dense tissue (muscle) will cause more loss than soft tissue (lungs). Very dense tissue (bone) causes rapid reduction in bullet mass into fragments.

Years ago, I shot a moose with a 7mm magnum. I recovered the bullet. It was made by the Nosler company, and its design was partitioned. That means the front expanding part of the bullet was separated from the back part by a copper partition. This design allows mushrooming of the bullet to stop at the partition, making sure a critical mass stays intact for deep penetration inside a big animal no matter what the bullet hits.

The unfired bullet weighed 175 grains, but after firing and recovery it weighed about 140. That means the bullet did its job. Approximately 35 grains of lead became small secondary projectiles inside the moose. Fragments of any shattered bone also became secondary projectiles.

So, two things damage the animal’s tissue. First, the bullet penetrating through flesh goes approximately in a straight line–the primary wound channel. Lead and bone fragments traveling in tangents from the bullet’s path destroy tissue deep inside the animal.

The second cause of tissue damage is the effect of the bullet’s energy (a product of its weight and velocity) transmitted to the animal. This is called the secondary wound channel. Tissue around the primary wound channel expands suddenly and concussively, which causes the rupture of muscle, blood vessels, nerves and bone that the bullet never touches. Although the tissue collapses back to its approximate original position, significant damage has been done a few inches outside the primary wound channel.

All of this usually provides an immediate kill, which is what hunters aim for. While shot placement is very important, the expanding bullet is what does the damage that helps hunters recover deer quickly, and usually close by.

Different bullets are designed for different results. Bullets designed for targets don’t do what hunting bullets do. Bullets designed for small animals don’t do what hunting bullets do. Bullets designed for war don’t do what hunting bullets do. Hunting bullets are designed to damage and disrupt every system–circulatory, nervous, and mechanical (muscular and skeletal). That’s how a hunting bullet causes a quick and merciful kill.

Shoot with accuracy because bullet placement is important. But hunting is not only about bullet placement, so shoot a bullet that’s made for the animal you’re targeting. No one is lucky enough to place the bullet perfectly every time, and when you don’t, a bullet made for the task will still do the job.

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When “The Everyday Hunter” isn’t hunting, he’s thinking about hunting, talking about hunting, dreaming about hunting, writing about hunting, or wishing he were hunting. If you want to tell Steve exactly where your favorite hunting spot is, contact him through his website, www.EverydayHunter.com. He writes for top outdoor magazines, and won the 2015, 2018 and 2023 national “Pinnacle Award” for outdoor writing.