How To Zero A Rifle Scope At 100 Yards [Beginners Guide] (2024)

Every year, thousands of sports-minded men, women, and youth flock to local gun ranges and other outdoor venues to sight in their favorite (and possibly only) scope sighted rifle.

For many, this is a frustrating experience. Hundreds of thousands of rounds are spent on this exercise which should be a straightforward and simple process.

As a gunsmith, hunter, dealer, and collector, I have zeroed hundreds of rifle scopes. With patience and a good process, you can have the same success that I get when zeroing a scope.

Regardless of what and how you are shooting, it's vitally important that you know your equipment and how it works.

Ethical hunting and safe shooting with a scoped rifle depends on the proper adjustment of the scope and rifle as well as a skillful and knowledgeable shooter.

If you are an advanced shooter looking for some hidden gem or as yet undiscovered insight into gun optics, this article is not for you.

If however, you are one of the vast shooting majority of casual shooters and hunters looking for a repeatable, effective method to sight in a rifle scope for general purpose use, stay tuned. This article has you covered.

Equipment, Let's Start At The Beginning.

If you already have a scoped rifle, I'll assume that you are going to live with the equipment you've got.

If you are looking to buy a general-purpose hunting/shooting rig, here are some quick recommendations to get you pointed in the right direction.

Choose The Right Caliber and Gun.

The average shooter does not need the latest Ultra-Hyper Big-Bore Super Magnum caliber. Choose a caliber that you can shoot comfortably in a cartridge that suits the game you hunt.

There are many easy-to-shoot cartridges which are widely available and the appropriate one will take any game in North America with the exception of the largest "dangerous game" species.

As far as the rifle goes, choose a bolt action, lever gun, or semi-auto that fits your build and style of shooting.

There are many great AR chamberings out there as well. If hunting, choose ammunition with a good hunting bullet and avoid bullet drop.

Choose the Right Scope

A good 3-9 x 40mm scope is a favorite of many hunters. It will get you well past 300 yards with the right cartridge which is fine for most deer hunting rifle needs.

Unless you have a particular need, larger, heavier, more powerful scopes won't make you shoot any better.

Go for quality and buy the best scope you can afford. Know your scope and its adjustments. READ THE BOOK!!

Some Quick Picks For A Good Basic Rifle Scope

1. Burris Fullfield E1 3-9x40 Ballistic Plex E1

2. Leupold VX-Freedom 3-9X40mm Rifle Scope

3. Sig Sauer Whiskey 3 Scope, 3-9X40mm

How To Zero A Scope At 100 Yards

First, we can get past all the jargon to what really matters in simple terms. Distance, volume, and almost any other property can be measured in many different units.

For angles, the two major units are the familiar degrees and the less familiar radians.

There are 360 degrees in a circle which are further sub-divided into 60 "minutes" of angle (MOA).That means that there are 21,600 tiny slices of the pie. At 100 yards each "slice" is equivalent to almost exactly 1 inch.

There are 6.28 radians in a circle (it's a convenient science/geometry thing, just trust me). Radians are further sub-divided into 1,000 parts (milliradians or MIL).

That's only 6,280 small slices and each slice is equivalent to 3.6 inches at 100 yards.

Each click of the windage and elevation adjustments on your scope almost certainly has one of the following adjustment values (divide by 4 to get the adjustment at 25 yards):

1/8 MOA = 1/8" at 100 yards (not very common very fine adjustment) = .0313" at 25 yd
1/4 MOA = 1/4" at 100 yards (common adjustment for MOA scopes) = .0625" at 25 yd
1/2 MOA = 1/2" at 100 yards (less common) = .125" at 25 yd
OR
1/10 MIL = .36" at 100 yards (about 1/3") = .090" at 25 yards = .0225" at 25 yd

Armed with that knowledge, here is a bullet proof way to zero your scope at 100 yards.

What you will need:

• Targets with 1" gridlines and an inches ruler.
• Staple gun or tape.
• A spotting scope or really good 10x plus binoculars are a big help but not essential
• A range with 25-yard and 100-yard stages. The 25-yard range IS essential unless you are checking zero on a previously sighted scope.
• A pocket calculator. Yes, you will need one.
• A proper fitting screwdriver if required by your scope turrets.
• Shooting bags or padded blocks.
• Printer paper

What To Do. Follow these steps for success.

I am going to assume that you have a new rig or scope that has not been previously sighted in and access to a shooting range.

We will start at the 25-yard range. If you have a laser bore sighted and are confident that you can get the scope "on paper" at 100 yards, then skip the 25-yard range.

Follow ALL of these instructions to zero a rifle and your patience will be rewarded.

Check Your Scope and Mounts

Check EVERY screw on your rings and mounts for tightness. Moderate finger pressure with the appropriate Allen, Torx, or other wrench is sufficient. Do not skip this step and don't over-tighten.

Sight in at 25 Yards

Post your target at gun level on the 25-yard range. Wear proper eye relief and hearing protection. Unless your scope is new out of the box, do the following.

Screw the turrets all the way in until they bottom out. Don't force them. Then screw them out until they bottom out the other way counting turns. Turn them halfway back in counting turns.

Adjust the ocular on the rear sight of the scope to obtain a sharp focus on the crosshairs.
If equipped with a parallax adjustment, obtain a sharp focus on the target or set to the minimum or zero distance.

Hold the rifle steady on shooting bags or rifle rest and fire one round at the bulls eye using low magnification.

Then go down range and measure the horizontal and vertical distance from the point of impact to the center of the target. Groups are generally not necessary for your first shots.

Do the Math!

Let's assume on the 25-yard range that your first shot was 1 3/4 inches right and 1 1/4 inches low.

Calculate the left clicks needed with a 1/4 MOA scope. 1.75 / .0625 = 28 clicks LEFT. Yes, that's right! Turn 28 clicks left.

Then calculate the up clicks needed 1.25 / .0625 = 20 clicks UP. Turn 20 clicks up. That should get you close.

Fire one shot on the center target to confirm the correction. It doesn't have to be dead center. If you are within 1 inch of the center, gather your gear and head over to the 100-yard range.

(NOTE: Most hunting calibers will actually shoot 1/2 to 1 inch LOW at 25 yards when zeroed at 100 yards. (You can adjust your zero low at 25 yards if desired)

Zero at 100 Yards

At 100 yards post your target at gun level. Then do yourself a BIG favor and surround the target on all sides with sheets of ordinary printer paper.

It's not unusual for a rifle sighted in at 25 yards to miss a 10 inch rifle target at 100 yards. The extra-large background will save you a lot of trouble on a target stand shot full of holes.

If equipped with a parallax adjustment, obtain a sharp focus on the target.
Steady the gun on shooting bags and fire one round at the center of the target using high magnification.

If you feel that the shot was good, there is no need to shoot a group at this time. Go down range and measure the horizontal and vertical distance from the center.

Do the Math Again!

Lets assume that the shot at 100 yards is 4 1/8" high and 3 1/2 inches left. Calculate the RIGHT clicks needed to adjust the scope. 3.5" / .25 = 14 clicks right. Calculate the DOWN clicks needed 4.125" / .25 = 16.5 (round to 17) clicks down to zero the scope.

Now you can shoot a 3 or 5 round group. Measure from the center of the group to the center of the target and calculate clicks as before if necessary to fine tune your zero.

What about groups? At 25 yards groups are just not necessary. Practice a good cheek weld steady breath control, a solid rest, and smooth trigger squeeze.

Call your shots. If you think you bobbled the shot, then by all means shoot again. At 100 yards you can make your initial correction with one carefully placed shot.

Then shoot for a group. Shooting groups burns up ammo, money, and your barrel. 

You can certainly zero your scope at a greater distance for long range shooting, but a 100-yard zero is a good starting point.

Check out an online ballistics program such as Shooters Calculator for zeroing at a longer distance.

What about the “one shot zero” method? One shot zero relies on shooting a test shot and then carefully adjusting the elevation and windage to bring the crosshairs onto the point of impact while holding the rifle absolutely motionless.

In theory, this works if you have a rifle rest and can hold the rifle motionless with one hand while adjusting the turrets with the other hand while looking through the scope.

If you bobble, you’re back to square one. If you are one of the few with the setup to do it, give it a try. The shoot and measure method works best for me.

Conclusion

That's it. I have sighted in hundreds of scoped guns over the years. Using this method of zero a rifle scope at 100 yards, I have rarely used more than 10 rounds to sight in an un-zeroed, unknown scope. 

The secret if there is one is patience and attention to detail. Don't estimate clicks, measure and calculate them.

Double check your calculations. Don't use the spotting scope to measure or estimate. Go downrange with a ruler and measure.

If your gun just won't behave, take it to a qualified gunsmith or armorer. Set realistic expectations. 

There was a time when a three-inch group at 100 yards was considered good-to-go. A vintage 30-30 with a 4x Weaver will probably not be an MOA gun but it will still bring home the bacon when zeroed properly and used within its limitations.

So get the right gear and go out there and zero your rifle!