When a shooter pulls the trigger, a series of events sets the bullet on its path toward the target. While shooting may seem straightforward, the science behind how a bullet travels is far more complex.
Understanding the basics of ballistics can significantly improve a shooter’s accuracy and performance. But what exactly happens between the muzzle and the target?
In this article, we’ll explain the fundamentals of ballistics in simple terms, helping you grasp how a bullet behaves in flight and how external factors like temperature, air resistance, and wind can impact its trajectory.
What is Ballistics?
Ballistics is the science of how projectiles move through space. In the context of firearms, it refers specifically to how bullets behave once they leave the barrel. Understanding ballistics helps shooters predict and control where their shots will land. Broadly, ballistics can be broken down into three categories:
- Internal Ballistics refers to what happens inside the firearm, from the moment the primer ignites the powder until the bullet exits the barrel. It involves factors like barrel length, barrel twist rate and the bullet’s muzzle velocity.
- External Ballistics – External ballistics take over once the bullet leaves the barrel. This part of ballistics deals with how the bullet travels through the air, encountering forces like gravity, air resistance and wind that impact its path.
- Terminal Ballistics – This final stage is when the bullet impacts its target. It encompasses how the bullet penetrates the target, its speed at impact, and the damage it can cause.
Each type is influenced by variables that a shooter can learn to control or account for during their shot.
Internal Ballistics – What Happens Inside the Barrel
Internal ballistics focuses on the bullet’s path from the chamber to the end of the barrel, and understanding this process is key to improving accuracy and firearm performance.
- Ignition of the Primer and Powder: When you pull the trigger, the firing pin strikes the primer, igniting the gunpowder inside the cartridge. This explosion creates high-pressure gas, which propels the bullet forward down the barrel.
- Bullet Movement in the Barrel: As the gas expands, it pushes the bullet forward. The rifling inside the barrel, which consists of spiral grooves, forces the bullet to spin. This spin stabilizes the bullet, making it more accurate as it travels toward the target.
- Muzzle Velocity: The speed of the bullet as it exits the barrel is called muzzle velocity. A higher muzzle velocity generally means a flatter trajectory, but it’s affected by several factors like barrel length and the type of ammunition used. Shorter barrels often produce lower muzzle velocity because the bullet has less time to accelerate before leaving the barrel.
Internal ballistics is important because it directly influences the bullet’s speed and stability as it exits the firearm. If the bullet doesn’t leave the barrel with the right amount of spin and speed, it won’t fly straight, no matter how well you aim.
External Ballistics – How Bullets Travel Through the Air
Once the bullet exits the barrel, external ballistics takes over. In this phase, a shooter’s understanding of environmental factors becomes critical, as various forces influence the bullet’s path to the target. Here’s what every shooter should know about external ballistics:
- Gravity: As soon as a bullet leaves the barrel, gravity pulls it downward. This is why a bullet doesn’t travel in a perfectly straight line but rather follows a curved path called a trajectory. Shooters must account for gravity, especially at longer distances, by adjusting their aim higher than the target.
- Air Resistance (Drag): As the bullet moves through the air, it encounters resistance, which slows it down. The shape of the bullet, its speed and even the air density (which can vary depending on altitude and weather) all affect how much drag the bullet experiences. Higher speeds tend to reduce the impact of drag initially, but the bullet will decelerate over longer distances.
- Wind: Wind is one of the most unpredictable factors in external ballistics. Depending on its direction and strength, it can push the bullet off course, either to the left or right. Shooters need to adjust their aim to compensate for wind drift, especially in long-range shooting, where wind can have a more significant impact on bullet flight.
- Spin Drift and the Coriolis Effect: While less of a factor in short-range shooting, spin drift and the Coriolis effect come into play over long distances. Spin drift occurs because the bullet’s rotation causes it to drift slightly to the side (usually to the right if the rifling twists that way). On the other hand, the Coriolis effect is the Earth’s rotation affecting the bullet’s path—again, a small factor unless shooting over extreme distances.
By understanding these external factors, shooters can adjust their aim and improve accuracy, even under changing environmental conditions. This knowledge is especially valuable for hunters and long-distance shooters who often contend with wind, drag and gravity over greater ranges.
Terminal Ballistics – What Happens When the Bullet Hits the Target
Terminal ballistics refers to a bullet’s behavior when it impacts its target, which is critical in hunting and personal defense. When a bullet strikes, its penetration depends on factors like velocity, bullet type and bullet design. For example, hollow point bullets are designed to expand upon impact, creating a larger wound channel while reducing the risk of over-penetration, which is ideal in self-defense. However, full metal jacket (FMJ) bullets penetrate deeper without expanding, which may be preferred in specific situations.
Energy transfer plays a key role in determining a bullet’s effectiveness on live targets. A high-velocity bullet with significant mass transfers more kinetic energy, leading to greater damage. This energy transfer can be the deciding factor in stopping a threat or ensuring a humane kill when hunting. As the bullet deforms or expands upon impact, such as with hollow points, it creates a wider wound channel and maximizes stopping power by dumping more energy into the target.
Upon impact, the bullet creates a temporary vacuum, or cavitation, that stresses surrounding tissues, causing additional trauma. The permanent wound channel left by the bullet reflects the path of destruction, damaging critical organs and blood vessels. The combination of energy displacement, bullet deformation and the resulting wound channel makes terminal ballistics a crucial consideration for hunters and those who use firearms for personal and home defense.
When Buying Ammo, What Ballistics Info Should I Pay Attention To?
When buying ammunition, understanding certain ballistic details can help you make the best choice for your specific needs, whether it’s for hunting, self-defense, target shooting or competition. Key information to look for includes:
Bullet Weight (Grains): This measures how heavy the bullet is. Heavier bullets, like 150-190 grains for a .308, offer deeper penetration and harder hits but have a more arched trajectory. Lighter bullets, such as 55 grains for .223, have a flatter trajectory but may not penetrate as deeply. Lighter bullets are better if you need fast, long-range accuracy; for closer ranges or larger targets, go for heavier bullets.
Muzzle Velocity: Muzzle velocity, usually measured in feet per second (fps), tells you how fast the bullet exits the barrel. Higher muzzle velocity gives a flatter trajectory, making it easier to hit distant targets, though the bullet decelerates faster. Look for higher velocities for long-range and flatter shots or lower velocity for controlled shots at shorter distances.
Muzzle Energy: This measures the bullet’s energy in foot-pounds (ft-lbs) as it exits the barrel. Higher muzzle energy translates to more impact force on the target, vital for hunting or self-defense. Look for ammo with higher muzzle energy if you’re after more stopping power. Lower muzzle energy might be sufficient for casual target shooting.
Ballistic Coefficient (BC) refers to a bullet’s ability to resist air drag, affecting how well it maintains speed and energy as it flies toward the target. A higher BC means the bullet flies faster, drops less, drifts less in the wind and delivers more energy upon impact. BC is influenced by the bullet’s weight, diameter and shape—the heavier, narrower and sleeker the bullet, the higher its BC. Bullets with high BCs look long, slim and pointy, with tapered boat tails designed for aerodynamic efficiency.
The ballistic coefficient becomes more important as the distance increases. Within 100 yards, it’s not a big concern—factors like accuracy and terminal performance (how the bullet behaves when it hits the target) matter more.
However, at 200 yards and beyond, BC starts to have a noticeable effect. By 300 yards, a higher BC can make a significant difference in trajectory and energy retention, making it crucial for long-range shooting. When selecting ammo for longer distances, you must balance accuracy, terminal performance and a bullet’s aerodynamic shape for maximum effectiveness.
If you’re using any type of ballistic calculator, then you’ll need to know all this information as well in order to get the most accurate firing solution.
Conclusion
Knowing how a bullet behaves inside the barrel, in flight, and on impact helps shooters at any level make adjustments for better results. Factors like wind, bullet weight & design, and bullet velocity all play a role, and by learning these basics, you’ll build confidence and hit your target more consistently.
Check out Ammo To Go, the ammunition retail sponsor of TTAG, for all of your ammunition needs.
Was this written by ChatGPT or another AI program?
Funny how competent subject matter experts are now commonly derided as being bots. Is it well known yet that there is a definite correlation to making that accusation and being a Harris voter?
Anyway, one of the more critical issues with choosing a firearm is to define what range it will shoot, and what target. IE, how far it has to go to strike the target, and for our purposes, is it paper, or live? THAT determines what cartridge to use – not the latest marketing push by influencers.
Sighting in then follows, if it’s paper at a known distance, it’s simple. Shoot small groups at a bullseye. If it’s a varying ranges, then the ballistic curve of flight creates an issue – do you correct your sights at the different ranges, or, do you even have the time? Fortunately, for shooting live targets, it’s NOT a matter of determining what fraction of a bullets impact you need to adjust. The target is often – as in deer hunting – a 18″ x 18″ rough square where vital organ disruption provides a stopping stop. No, we do no guarantee it will stop them dead right there, but we do want to ethically prevent losing game who run off and hide.
Same for two legged opponents – it’s a center of mass 18″ x 18″ target that should stop their continued effort to shoot back. That is the goal, first and foremost, nothing more, and it’s hard enough to accomplish it. At various random ranges, it’s also much easier to put an effective round inside that center – it’s so big a calm dispassionate shooter of adequate skills should hit it out to the maximum “effective” range of that cartridge.
For most hunters after deer, that’s about 350 yards, give or take, and sighting in to hit inside that by putting the sights on center mass should do it. That means understanding where the bullet starts to drop excessively, causing hold over, ie you have to aim high to the point it causes misses. Since most of the bullet drop is at the further end of trajectory, sighting in two inches high at 200 yards averages out for many cartridges to still hold dead on out to 350. That’s a generality, 5,56 vs .458 are going to have different ballistic curves. Larger bullets drop a lot more at the end of their trajectory, we are just trying to take advantage of the curve to the best application.
That is how you do it for maximum “effective” range on live targets, and many would be much better off instead of fiddling with sights and scopes. Put the crosshairs dead on and shoot – within the limits of that ballistic curve.
It then goes to, how much magnification you really need, vs want, and for a general rule, about 1 power per 100 yards should do it. Yes, I bought a 3×9 variable for a .30-06 deer rifle – but for the most part, shots at 3X were also a bit hard to see which end of the fur I was aiming at. 9x isn’t usable under 400 yards much, unless it’s a wide open prairie with a critter sunning themselves, stationary. In broken woodlands, iron sights on a .30-30 were more than sufficient to endanger whitetail to the point of eliminating them from North America – not what many think.
Don’t let the influencers push you into the latest sales marketing, determine your range and target, then what ballistics delivers the best application – not the most popular currently – and match the scope to the job, not what is “recommended” by media paid to market them.
Negative. This wall all input from a few distance shooting professionals.
Lighter bullets better for distance?
No. Distance, but loss of accuracy.
I learned a few things from this. Will read it again.
Last week, I was changing springs in some magazines. Working at the kitchen table, I bent a spring. Since I did not want to put the old spring back in, I loaded the ammo into a empty vitamin bottle.
That afternoon, my wife was somewhat annoyed with me.
Wait… so you’re saying JUST that afternoon?
Unicorn Whisperer,
Well…………
MY wife is NEVER annoyed by ammo or gat related purchases. She’s my favorite spouse🙂
Your favorite spouse? How many do you have?
Wow.
So you actually know the reason your wife was annoyed with you.
Must be nice.
Genius comment
“…empty vitamin bottle.”
Pills are pills, don’t see a problem here?
But then, my eye is still swollen shut from the last time I didn’t see a problem…
That aside, I can tell you, a 20 dram pill bottle is perfect for carrying 3 moon clips of 9mm in the backpack, for the LCR.
You dont pull the trigger. You squeeze the trigger. If I am shooting out to 1000 yards I am using a .308WIN 175grn Lapua Scenar-L or Nosler RDF. Not a light weight .223REM. You forgot to mention bullet jump.
I think pull makes more sense. Just sayin
One thing nice about a round ball is it never tumbles, point first always.
uhhh. lighter bullets better for long range you? says you.
Aside from heavier bullets generally bring superior to lighter bullets depending on drag coefficient, aerodynamic drag is far greater at higher velocities than at lower velocities. This is why heavier bullets are generally favored for longer range shooting.
BTW, the same considerations apply to shotguns. The potential range of shotgun projectiles is primarily a function of the diameter, mass and sectional density of the projectile. A few centuries ago a French artillery officer conducted systematic experiments to determine how far various spherical projectiles that were fired from cannon at lofted trajectories would fly. The result was Journee’s Formula. The potential range of a projectile is approximately equal to the diameter of the projectile measured in inches or fractions there of multiplied by 2,200 yards. Journee’s formula is reasonably accurate for anything from Bee Bee guns to battleship guns provided one makes corrections for drag coefficient and sectional density of the particular projectile type. Corrections for reduced atmospheric density at higher altitudes are also relevant. Of course for very large caliber artillery, reduced aerodynamic drag from the thinner atmosphere at altitude becomes significant.
Ballistics for dummies is right. I actually read an argument trying to explain that the reason police were unable to determine if a suspect inside a car attempted to fire through the windshield was because the bullet from the suspect’s handgun was unable to achieve sufficient velocity and power to penetrate the window from the inside because of the limited distance between the handgun and the window. (Actually his explanation was shorter, but just as stupid, Undoubtedly the commentor held a Phd. in physics from Fb University or maybe saw Bugs Bunny stick a carrot in Elmer’s shotgun barrel.)
I actually had imbecile Judge Ladd Wiles give my marijuana bootlegging tenant a free pass for shooting at my son with a 12 gauge shotgun loaded with slugs because his sleazy, semen sucking attorney utilized a similar argument. He put a marijuana bootlegger on the witness stand and misrepresented him as a “gun expert”, citing the fact that he “builds” illegal, short barrelled, AR-15 ghost guns that are converted to full automatic. This idiot then testified that my tenant could not have been shooting slugs because his Remington 870 had a choke. If he had been shooting slugs, “the barrel would have exploded just like happens to Elmer Fudd when Bugs Bunny sticks a carrot in the muzzle of his shotgun.”.
This is why I am a staunch advocate of Shoot, Shovel and Shut up. Unless you live in a deep red, conservative community, you should never, ever call 911.
Perhaps the perpetrator was armed with a Rocket Propelled Grenade launcher or a Gyrojet pistol that fires miniature rockets?
“Coriolis Force”?
Nope. I think the author was thinking of the Magnus effect.
The Coriolis effect is applicable depending upon what direction, North, East, South or West the bullet is fired and on what Latitude the shooter was at.
I’m sorry for being rude, but this article is so badly flawed that it is an abomination. Aside from maybe getting someone killed, this misinformation will be exploited by y sleazy attorneys to get their client exonerated for shooting incidents.
There are books written on this…read them. David Tubb, Jeff Siewart, Brian Litz, etc.
There are also many on line ballistics calculators. Most of them might utilize algorithms and source code that I wrote back in the day in Fortran on punch cards.
I highly recommend Tiborasouras’ “Sniper 101” Youtube series. Bad name, but really good info that’s easy to digest.
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