Sighting in a rifle ahead of hunting season is a relatively simple process. Different people have different methods, but one commonality you’ll see a lot is that many hunters like to sight their rifles in so that the bullet impacts about an inch or two above the bullseye at 100 yards. This seems counterintuitive at first glance, especially to newer hunters and shooters. Why wouldn’t you want your gun to hit the bullseye at which you’re aiming?
First of all, many hunters only have access to a 100-yard range, so the 100-yard zero isn’t arbitrary—it’s the physical limit of what they have to work with. And, although data is hard to come by, the internet generally agrees that about half of the white-tailed deer shot in North America are taken at distances of 100 yards and under, so it’s a solid number.
But second, and more importantly, sighting in an inch or so high at 100 yards allows you a larger margin when you’re shooting at a deer or similar-sized game. To understand why this is true, you need to know how a bullet’s trajectory works and how your scope is aligned with it, and you need to know a basic fact about the vital zone on a deer. Three points here:
- When a projectile leaves the muzzle of a gun, it travels not in a straight line, but in an arc—first rising briefly, then beginning to fall as gravity pulls it to earth. Technically, it’s not actually rising in relation to the muzzle—it’s falling from the moment it leaves the gun—but it’s rising in relation to the scope’s line of sight, because the scope is angled slightly down and the muzzle is angled slightly up in relation to each other. Just … trust me.
- Your scope’s line of sight will line up with the target at two points in the projectile’s flight. The first is early in the flight, in the vicinity of the 40-yard mark depending on the load. The second intersection of line of sight and projectile flight is what we’re talking about here. By now the bullet is falling in relation to the scope’s line of sight, and however far away that intersection/target is represents the distance at which your rifle is zeroed. Imagine a straight line going out from your scope and an arc going out from the muzzle. The second point at which the two lines intersect is where you are zeroed, and since this is on the downward side of the arc, the bullet continues to fall past the zeroed distance.
- The vital zone (heart/lung area) on a white-tailed deer is approximately an 8- to 10-inch-diameter circle, or about the size of a paper plate. Using 8 inches to be conservative, if you hold your crosshairs in the middle of the vital zone, you have about 4 inches beneath your hold point that represent a good kill shot.
What this means is that if you zero your rifle to impact the bullseye at 100 yards, your bullet will impact an inch or two or three (depending on the load) below the bull’s-eye at 200 yards. Using a 175-grain 7mm PRC bullet I recently killed a deer with as an example, I can plug the rifle and load data into my Hornady ballistics app and see that zeroed at 100 yards, my bullet impacts as follows:
- .21 inches low at 50 yards
- Dead on at 100 yards
- 02 inch low at 150 yards
- 42 inches low at 200 yards
- 4 inches low at 250 yards
- 17 inches low at 300 yards
Zeroing your rifle an inch or two high at 100 yards is, depending on your bullet, essentially the same as zeroing it dead-on at 200 yards. This is hunting, not precision shooting, so while you should know your rifle and load’s numbers specifically, “an inch and a half high at 100” has kind of become the pretty-close-to-zeroed-at-200 standard that most hunters have just rounded off to over the years. Depending on the bullet, this could be more like 2 to 3 inches, so again, know your numbers.
Using my app, I can see that if I zero my rifle at 200 yards, the numbers from above shift to look like this:
- .65 inches high at 50 yards
- 71 inches high at 100 yards
- 55 inches high at 150 yards
- Dead on at 200 yards
- 12 inches low at 250 yards
- 03 inches low at 300 yards
Now, remembering that the vital zone on a deer is maybe 8 inches in diameter, you can see that zeroing at 200/zeroing high at 100 gives us a much broader range wherein we can just hold the crosshairs right in the middle of a deer’s vitals and expect a good hit. In this example, with a 100-yard zero, if you hold in the middle of the vitals, you can shoot out to about 200 yards before the bullet drops below the vital zone. If you jerk the shot a little high, you’re OK at that distance, but if you jerk it a little low, you’re probably in trouble, because you’ve already maxed out your margin for error.
However, if you’re zeroed at 200/zeroed a bit high at 100, you can hold your crosshairs in the middle of the deer’s vitals at 50 yards all the way out to 250 yards before you even approach the bottom of the vital zone, and you still have an inch or two of leeway for a jerked-low shot at 250. Even at 300, if you’re a good shot and you have practiced this at the range, you can hold at the top of the vital zone (or slightly above) at 300 and the bullet has plenty of room to drop into the vitals.
And all of that data is using the 7mm PRC, which is a fast, flat-shooting cartridge. If you’re using something slower, your bullet drops faster, making a 200-yard zero even more versatile. For example, a 160-grain .30-30 Win. Hornady Lever Evolution bullet zeroed at 100 yards will impact 2 inches low at 150 yards and 6 inches low at 200 yards. At 200 yards, you’re already well past the point of being able to hold in the middle of the vitals if you’ve zeroed this gun at 100 yards. If you zero it at 200 (which in this case is 3 inches high at 100), the bullet is 4.9 inches low at 250 yards, which is just off the vital zone if you hold dead-center, but at least you can shoot confidently out to 200 without even having to think about holdover.
The bottom line is that zeroing your rifle a little high at 100 yards simplifies your mid-range shooting by letting you hold directly on the vital zone farther than you could if the gun was hitting dead-on at 100 yards. You can shoot at farther distances without having to worry about holding the crosshairs higher on the animal’s body. “An inch or 2 high at 100” will get you pretty close to that 200-yard zero you’re looking for, but plug your rifle and load’s numbers into a ballistics calculator or at least read the drop numbers on the box of ammo to know exactly how high you want to be at 100 in order to be dead-on at 200, and to know how far the bullet drops after that if you plan to shoot past 200. And, if at all possible, actually shoot your rifle at 200 yards and beyond to verify that those numbers hold true in real life.