Ballistics 101: Drop and Drift and Why They Matter

The more you shoot, the more you’re likely to realize there are numerous factors at work when it comes to the ammo you’re using. You begin to discover things like the bullet’s shape, the bullet’s weight, and the powder behind it all affect the outcome. Then there’s drop and drift. Do those things really matter to you if you’re not a long-range shooter? Do drop and drift even come into play at short distances or with handguns? The answer to both questions is yes, drop and drift matter, and the greater your understanding of how they work, the better your results on target will be. We will look at what drop and drift are, what affects them, and what that means to you as a shooter.

bullet trajectory
Drop and drift have to do with the bullet’s trajectory, which is illustrated here. [Photo credit: Quora]

Drop and Drift Rate?

Drop and drift are common terms used regarding bullets that can be explained both simply and incredibly in-depth. For this article, we’re going with the easier-to-understand route.

Drop refers to how a bullet loses height vertically during its trajectory; drift refers to the bullet’s movement to one side or another along a horizontal plane along that same path. The two happen simultaneously, meaning the bullet both loses height and begins to drift to the side all at once.

What Affects Drop and Drift?

Many things affect the drop and drift rate. Factors include the bullet weight, bullet type, wind, and more. As you might have guessed, a heavier bullet will generally drop at a faster rate than a lighter one. However, that higher weight can also help it drift more slowly because it’s better able to resist the push and pull of the wind. Taking that a step further, the barrel length and powder in the specific load also matter when it comes to the velocity at which it begins its journey—and, in exchange, the resulting speed of the drop and drift rate.

What is Spin Drift?

Another term you’re likely to hear that applies to drop and drift rate is spin drift. Spindrift—also called gyroscopic drift—is the way the bullet responds to the usual righthand twist rate of the gun. Thanks to that righthand twist, the bullet exits the barrel of the gun with a preference leaning to the right, something that becomes more pronounced at greater distances. Keep in mind that wind is going to affect this as well, but taken on its own and applied to a righthand twist—which most guns have—spin drift just means the bullet is being encouraged to travel to the right. It is possible to calculate the spin drift of a particular bullet, and it’s something worth doing as you get more involved in ballistics and long-range work.

coriolis effect
What is the Coriolis Effect, and why does it matter for gun owners? [Photo credit: Encyclopedia Britannica]

What’s the Coriolis Effect?

The Coriolis Effect is another part of drop and drift, and the answer to what it is is two-fold. First is the general scientific definition. The Coriolis Effect refers to physics and has to do with the way the earth rotates on an axis.

Due to how it rotates, the air currents deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. What does this mean? This means that the physics of the earth’s rotation affects how objects with masses that are not on the ground travel. The force involved in the Coriolis Effect deflects that object, so it moves along a curving path. As you might have guessed, it would be easy to get off into the weeds of gravity and other things here, but let’s move on.

How this impacts bullet trajectory is that the Coriolis Effect has an effect on the curvature of the bullet’s trajectory. In a broad sense, you could say it makes the target move away from the bullet due to the way the bullet is deflected along its path. This has a much more significant effect on precise long-range shots than on the average guy shooting at the range. Even so, it’s worth having a basic understanding of it.

9mm ammo
Drop and drift matter whether you’re shooting handguns or rifles. [Photo credit: Sellier and Bellot]

What Does Drop and Drift Mean to You?

What drop and drift mean to you as a gun owner depends on what you’re doing. Drop and drift always happen, just to a lesser degree at shorter distances. If you’re shooting long distances, you’ll spend a lot more time learning about drop and drift and the associated calculations. However, that doesn’t mean it has nothing to do with handguns.

Recently, a small-town gun range received a complaint that a nearby resident’s property was being struck by bullets. The resident claimed they’d seen these bullets strike solid, rigid objects in their yard with enough force to break said objects, which had significant mass. Obviously, if this was happening, there was a serious problem. Here’s what this has to do with drop and drift.

These supposed stray bullets were said to be 9mm FMJ, and the resident’s house was well over 1,000 yards from the range. Let’s say that 9mm had a 115-grain bullet, which is relatively common among target ammo. When you’re making calculations, there are all kinds of things to consider, from bullet weight to muzzle velocity to the temperature and humidity on the day in question. Taking those factors into consideration when calculating the likely drop rate of a 9mm 115-grain FMJ, here’s what we get. Shooting at a target 10 yards away, the drop rate isn’t much. But by the time you hit 100 yards, it’s dropped about 4.3 inches. This increases quickly—by 500 yards, the bullet has dropped 473.7 inches, and by 1,000 yards, it would have dropped 3,067 inches. In addition, the bullet loses energy rapidly. If it started with 362 foot-pounds of muzzle energy, by 1,000 yards, it’s been reduced to approximately 47 foot-pounds. For comparison, the average human punch is typically around 80 foot-pounds unless they’re trained and manage to get that over 100 foot-pounds.

Bottom line? When you understand and calculate drop and drift, you realize the drop rate of this 9mm 115-grain FMJ being fired from a handgun with a 4.0-inch barrel at 1000 yards is equivalent to 255.58 feet. This includes remembering the shot was first fired at a bull’s eye from ten yards, and there isn’t 255 feet of space between the bullet and the ground—not even when you take the Coriolis Effect and curvature into consideration. You can see how understanding ballistics matters.

As a gun owner, understanding ballistics helps you figure out how to sight or zero to get on target. If you’re shooting handguns, the drop and drift aren’t as extreme, but due to the way handgun calibers work, you are going to notice a bigger difference even at 50 and 100 yards (it can be a lot of fun shooting steel at 100 yards with a handgun). There are a lot of fascinating aspects to firearms, and when you take an interest in ballistics, you will discover practically endless information. And the more you learn, the more you become a better shot. Whether you’re a self-defender, hunter, or long-range shooter, these things matter. Take the time to take an interest in the science behind shooting. You might find out it’s actually pretty enjoyable, and the end results in improved precision are well worth the investment of time.

Kat Ainsworth Stevens is a long-time outdoor writer, official OGC (Original Gun Cognoscenti), and author of Handgun Hunting: a Comprehensive Guide to Choosing and Using the Right Firearms for Big and Small Game. Der Teufel Katze has written for a number of industry publications (print and online) and edited some of the others, so chances are you've seen or read her work before, somewhere. A woman of eclectic background and habits, Kat has been carrying concealed for over two decades, used to be a farrier, and worked for a long time in emergency veterinary medicine. She prefers big bores, enjoys K9 Search & Rescue, and has a Master's Degree in Pitiless Snarkastic Delivery.

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