Weapons & Marksmanship Fundamentals Core

Ballistics Fundamentals

Lesson 27 of 60 · Module 4, lesson 6

Your objective

By the end, you'll be able to explain trajectory, drop, zero, and terminal energy well enough to know your bullet's path and make a clean, ethical shot.

Concept ~8 min

You’ve zeroed your rifle dead-on at 100 yards. A buck steps out at 250. If you hold right on his vitals and squeeze, where does the bullet actually hit? Lower than you think — because a bullet doesn’t fly in a straight line. Understand the arc, and you make the shot. Ignore it, and you shoot under him. This lesson is that arc.

Quick recall

Quick recall from Rifle & Caliber Fundamentals — what does a rifle's 'caliber' roughly describe?

Roughly the diameter of the bullet (and bore) The exact killing power of the cartridge

Show answer

Correct: Roughly the diameter of the bullet (and bore) — Right — caliber describes the bullet/bore diameter. Bullet weight and the powder charge then drive its speed and energy, which is where ballistics begins.
Not quite: The exact killing power of the cartridge — Not quite. Caliber is mostly a diameter; the bullet's weight, speed, and construction determine its energy and effect — that's what ballistics covers.

A shot has three stages

“Ballistics” sounds like physics class, but for a hunter it’s just three stages of one shot. Name them and the whole topic gets organized:

Internal ballistics — everything inside the firearm from the primer firing until the bullet exits the muzzle: ignition, pressure, the bullet accelerating down the bore (NRA Family, Ballistics Made Simple).
External ballistics — the bullet’s flight to the target, shaped by gravity, drag, and wind (Hornady, External Ballistics). This is the arc you aim along.
Terminal ballistics — what the bullet does on impact: how it expands, transfers energy, and penetrates (Hornady, Terminal Ballistics). This is what actually kills.

As a hunter you mostly care about the last two: where the bullet goes, and what it does when it gets there.

The bullet arcs — and crosses your sight line twice

Here’s the idea that fixes the most missed shots. Gravity pulls on the bullet the instant it leaves the muzzle, so its path is a curved arc that always falls below the bore (Hornady, External Ballistics). To fight that drop, the barrel is aimed slightly upward relative to your line of sight. So the bullet launches upward across your sight line, peaks, and falls back down across it again — it crosses your line of sight twice. The second crossing is your zero.

Diagram comparing a straight horizontal line of sight with the curved bullet path. The bullet rises above the line of sight, peaks, then falls back through it at the zero distance, and continues dropping well below it farther out. — Diagram (not to scale). Dashed line = your line of sight. Curved line = the bullet's arc. It crosses the sight line at the zero, then keeps dropping — that drop is what you hold for at long range.

Deep dive What is a 'zero' and how far should I set it?

Zeroing (sighting in) means adjusting your sights so your point of aim equals your point of impact at a chosen distance (Texas Parks & Wildlife, Sighting In). A 100-yard zero is the common starting point. Some hunters zero an inch or two high at 100 so the bullet stays near center out to ~200 yards — a way of using the arc. Taken further, your maximum point-blank range (MPBR) is the distance over which the bullet never rises or falls outside the vital zone when you aim dead center; for many deer cartridges that’s around 250–300 yards (American Hunter / NRA, MPBR). The exact dialing-in belongs to the Sighting-In & Zeroing lesson — here, just know that a zero exists and the bullet drops past it.

Edge case Ballistic coefficient — why some bullets shoot flatter

A bullet’s ballistic coefficient (BC) is a single number describing how well it resists air drag. A higher BC means the bullet slows down less, so it flies flatter and keeps more velocity and energy downrange (Hornady, Ballistic Coefficient). It’s why a sleek, pointed bullet outperforms a stubby one at distance. You don’t need to compute it — just know that a higher-BC bullet drops less at the same range.

Energy, and why the bullet has to expand

Reaching the deer isn’t enough — the bullet has to arrive with the energy to kill and the design to use it. Kinetic energy is KE = ½ × mass × velocity². Because velocity is squared, speed matters more than weight, and energy bleeds off with distance as the bullet slows. A frequently cited rule of thumb is roughly 1,000 ft-lbs of energy at impact for deer — useful as a guideline, not a hard law; bullet construction and shot placement matter just as much (Outdoor Life, killing energy).

On impact — terminal ballistics — a proper hunting bullet expands (mushrooms). A soft-point, polymer-tipped, or bonded bullet opens up, transfers its energy into the animal, and cuts a larger wound channel than its starting diameter (Hornady, Terminal Ballistics). But expansion needs adequate velocity — so a bullet that’s dropped below its expansion speed at long range may pencil through without doing its job. As Hornady puts it, expansion is beneficial, but penetration is essential to reach the vitals.

Read the arc in the field

Decision

Your rifle is zeroed dead-on at 100 yards. A buck stands broadside at 250 yards. You hold your crosshair right on the center of his vitals. What happens?

It hits right where I aim — the scope is zeroed

No. The zero only guarantees impact at 100. At 250 the bullet has dropped well below your line of sight, so this shot lands low — likely under the chest. You have to account for drop.

It hits low — the bullet has dropped past my 100-yard zero

Right. Past the zero the arc falls away. At 250 you'd need to hold higher (or dial) to put it in the vitals. You read the arc correctly.

Check your understanding

Knowledge check

Why does a bullet cross your line of sight TWICE on the way to a distant target?

The barrel is angled slightly up, so the bullet rises across the sight line, then gravity pulls it back down across it The bullet bounces off the air and rises again Wind pushes it up and then down

Show answer

Correct: The barrel is angled slightly up, so the bullet rises across the sight line, then gravity pulls it back down across it — Right. The upward bore angle launches it above the sight line; gravity brings the arc back down through it at the zero. Two crossings.
Not quite: The bullet bounces off the air and rises again — No — a bullet only falls once it's launched. The two crossings come from the upward barrel angle plus gravity, not bouncing.
Not quite: Wind pushes it up and then down — Wind moves a bullet sideways, not up and down in a predictable arc. The two sight-line crossings come from bore angle plus gravity.

Knowledge check

Which stage of ballistics is about the bullet EXPANDING and transferring energy into the animal?

Terminal ballistics External ballistics Internal ballistics

Show answer

Correct: Terminal ballistics — Right. Terminal ballistics is the impact stage — expansion, energy transfer, and penetration into the vitals.
Not quite: External ballistics — External is the flight stage (drop, drag, wind). Expansion on impact is terminal ballistics.
Not quite: Internal ballistics — Internal is inside the barrel (ignition and acceleration). Expansion on the animal is terminal ballistics.

Take it to the woods

Know your trajectory before the season

0/5

I know my exact zero distance (e.g., 100 yards) and have confirmed it on paper.
I have a simple drop chart or dialed dope for my load at 200, 250, and 300 yards.
I checked that my bullet still carries killing energy (rule of thumb ~1,000 ft-lbs for deer) at my max distance.
Safety I set a personal maximum range where I KNOW both my drop and my energy — and will pass beyond it.
I'm using an expanding hunting bullet (soft point / tipped / bonded), not a target or FMJ bullet.

Sources

NRA Family, Ballistics Made Simple (three branches) — https://www.nrafamily.org/content/ballistics-made-simple/
Hornady, External Ballistics (trajectory, drop, line of sight) — https://www.hornady.com/team-hornady/ballistic-information/ballistic-resources/external-ballistics
Hornady, Terminal Ballistics (expansion, energy transfer, penetration) — https://www.hornady.com/team-hornady/ballistic-information/ballistic-resources/terminal-ballistics
Hornady, Ballistic Coefficient — https://www.hornady.com/bc
Texas Parks & Wildlife Hunter Education, Sighting In (zero) — https://tpwd.texas.gov/education/hunter-education/online-course/shooting-skills/sighting-in
American Hunter (NRA), How to Zero for Maximum Point-Blank Range — https://www.americanhunter.org/content/how-to-zero-your-rifle-for-maximum-point-blank-range/
Outdoor Life, Killing Energy: How Much Do You Need? (deer rule of thumb) — https://www.outdoorlife.com/blogs/gun-shots/2013/10/killing-energy-how-much-do-you-need-big-game/

If you remember nothing else

Ballistics has three stages: internal (in the barrel), external (in flight — drop, drag, wind), and terminal (on impact — expansion and energy transfer).
Gravity acts the instant the bullet leaves the muzzle, so the path is an arc, not a line. The barrel points slightly up, so the bullet crosses your line of sight twice.
Your zero is the distance where point of aim equals point of impact. Know it, and know how far the bullet drops past it.
Velocity matters more than mass for energy (KE = ½mv²), and energy bleeds off with distance. Roughly 1,000 ft-lbs at impact is a common rule of thumb for deer — a guideline, not a law.
A hunting bullet must arrive fast enough to EXPAND and still penetrate to the vitals. Know your trajectory, zero, and retained energy at the range you'll actually shoot.

How ready do you feel?

How ready are you to explain where your bullet goes between the muzzle and the deer — and why it still hits hard enough to kill cleanly?

Before you go — a quick look back

Distributed practice: one fast recall from an earlier lesson keeps it from fading.

Quick recall

From Firearms Safety & The Four Rules — Rule 4 is 'be sure of your target and what is beyond it.' How does a bullet's trajectory make that rule matter even more?

Show me the answer

Show answer

Correct: Show me the answer — A bullet doesn't stop at the deer or fall straight down on a miss — it keeps flying on its arc and can travel for over a mile. Knowing the projectile's range and path is exactly why you must know what's beyond your target before you ever fire.

Done with this lesson?

Mark it complete to track your way through the path. Saved on this device — no account needed.