Adjusting or zeroing a rifle can be a daunting experience for some shooters. I have heard some hunters compare the adjustment process to “black magic.”
This is hardly the case. Once a rifle shooter understands a few basic terms, the technical details of your scope, and a clearly defined goal, scope adjustment can be almost painless.
Zeroing a scope involves adjusting the scope so that the bullet strikes at a pre-determined point at a given distance. Once this point, known as “zero,” is found and set, subsequent windage adjustments and elevation adjustments can be made to compensate for factors such as distance, wind, and angle of attack.
Having a known point of impact is the critical goal of scope adjustment. The most expensive scope you can buy is no better than the adjustments that you make to bring the reticle to zero.
For long-range shooting, adjustments are critical. All of these adjustments are based on a properly adjusted scope with a known point of impact.
Understanding your Rifle Scope
I always urge my students and customers to start with a thorough review of the scope’s manual. While all rifle scopes share the same basic features and operation, manufacturers often make small but critical changes to how their adjustments work.
Before you even mount your scope, you should be completely familiar with its features, functions, and operation.
Before we move into the actual process of how to adjust a scope, let’s spend a little time on terminology, parts, and operations that tend to be common to all rifle scopes. These are the terms and the parts with which you should be familiar before starting your new scope experience:
The Body of Rifle Scopes
This one is pretty obvious. The scope body is the tube of the scope that serves as the platform for all of the other parts. The body of the scope provides the rigidity to be accurate, the ruggedness to withstand the rigors of hunting and shooting, and the mounting point for the scope to the rifle.
The Ocular Lens
The Ocular lens is the glass through which you look when using the scope. This lens is housed in the ocular lens housing and is the last point where the light passing through the scope is handled before it goes to your aiming eye.
The Objective Lens
At the end of the scope opposite the ocular lens is the objective lens. On most scopes, the objective lens is larger than the ocular lens and is housed in the objective lens housing. This lens is tasked with gathering and focusing the light from your target into an image that is passed through the scope to your eye.
The Ocular Lens and Ocular Focus Adjustment
Commonly referred to as the “eyepiece” of your scope, the ocular housing is attached to the scope body and may have several different functions, including ocular focus adjustment knobs.
On some scopes, the entire ocular housing turns to focus the ocular lens. Others may have a separate outer ring that turns around the ocular lens housing.
The Magnification or Power Adjustments
If your scope features adjustable magnification, it will usually be fitted with a ring around the scope body that allows the magnification adjustment in or out as needed.
Some magnification adjustment rings are graduated with numbers for quick reference about the magnification setting. Many more expensive, tactical-style telescopic rifle scopes have levers on the adjustment rings to make variable scope adjustments easier.
The Windage and Elevation Turrets
Every scope has two knobs called turrets located near the middle of the scope body. Usually, the top turret corresponds to the elevation adjustment. The side-mounted turret corresponds to the windage adjustment.
Turrets come in various styles that allow quick turret adjustments or with caps to protect the turrets from the weather.
The Parallax Adjustment Knobs
Some higher quality and more expensive rifle scopes have another adjustment knob that is used for target focus. This knob moves the internal scope parts to bring the image of the target into focus with the reticle of the scope.
This feature may be called a side focus or side parallax adjustment on some scope models.
The image you see in your scope that provides the point of aim on your target is the reticle. Reticles vary from simple cross hairs or illuminated dots to complex arrangements of lines, bars and range graphs to aid in range estimation for extreme long-range shooting.
Point of Aim (POA) and Point of Impact (POI)
The first and most critical goal of adjusting your scope is to ensure that your point of aim (POA) and your Point of Impact (POI) are the same at a given distance. Once the POA and POI at a known range are the same, the rifle is said to be zeroed. From this zeroed setting, compensations for different distances, wind conditions, and angles of attack can be calculated and dialed in as scope adjustments.
While this seems almost insanely easy, it is, in fact, a function of many variables that must be considered. Distance to the target is, of course, a primary factor. Bullet weight, bullet velocity, and ballistic characteristics all figure into the calculations. Fortunately, we don’t need to perform these complex mathematical exercises since most ammunition and bullet manufacturers provide this information.
Understanding Ballistics and Bullet Path
Unfortunately, bullets don’t travel in a perfectly straight and level line when they exit the muzzle of our rifles. As soon as the bullet leaves the rifle, gravity and wind resistance start to have effects. These two factors slow the bullet as it flies through the air and cause the bullet to drop along a curved line. This is called the trajectory and is the largest factor in scope adjustment.
The goal is to adjust the rifle scope reticles so that the bullet trajectory intersects the intended target at the aiming point of the reticle.
In theory, this can be calculated using sophisticated mathematical techniques. In practice, most rifle shooters do this using what amounts to a trial and error process known as “zeroing a rifle.”
It is easy to see in the illustration that the bullet travels a curved path to the target while the scope focuses on a direct line to find the aiming point. To ensure that the POI and the POA are the same, the scope must be adjusted to give the proper handle of departure for the bullet.
Properly Adjusting a Scope
There are no arcane secrets to adjusting a scope. If you adopt a systematic process, you can often adjust a rifle scope in under an hour of range time.
Zeroing your rifle doesn’t have to be an all-day tortuous exercise that leads to frustration. A few simple tips and preparation can make your scope adjustment time almost painless. After all, you get to go to the range and spend some time.
It All Starts with the Scope Mount
You can spend an inordinate amount of time trying to zero your rifle scope. However, if the scope is poorly or improperly mounted to the rifle, all of your efforts may be in vain. Zeroing your scope and rifle starts with properly mounting the rifle scope to the receiver of the rifle to ensure that the two perform together.
Level and Parallel
Your scope must be mounted to your rifle receiver so that the bore of the rifle scope is in line with the bore of the barrel. The scope must align in both directions with the bore of the rifle to ensure that the POA and POI are aligned. If the rifle scope is not properly aligned with the rifle barrel bore, it will be almost impossible to adjust a rifle scope to zero.
Secure and Stable Mounting
Secondly, the optics mounts must be secure and stable. Properly installed mounts ensure that the scope and rifle function as one unit. There should be no play or movement between the scope and the rifle when the mounts are secured. No rifle scope can be properly adjusted and be expected to retain a zero position if there is movement between the mounts and the rifle.
Select your scope mounts carefully, and be sure you get the right size scope rings. Typically scope tubes come as one-inch tubes or 30mm tubes. Your rings should be sized appropriately for a proper fit. Many serious shooters lap their scope rings before mounting their scopes to ensure that the rings are perfectly aligned and have smooth interior surfaces.
Positioning the Scope Properly
When placing the scope in the mounts, the distance from the ocular lens to your eye is crucial. All scopes have eye relief, which is the distance from the ocular lens to your eye that ensure the entire field of view is seen in the optic. Your scopes manual will give you the eye relief required on your optic. You should mount the scope so that when you shoulder your rifle in your normal shooting position, the eye relief is correct.
If you position the scope forward and increase the eye relief, you may not see the full field of view provided by your optic. Setting the scope too far back may result in a nasty bit of work called scope bite. The ocular lens housing can impact your eye or forehead, which is no fun and can end a great day of shooting with a trip to the emergency room for stitches.
The other mistake I see often on mounted scopes is that the reticle is out of alignment. This occurs when the optic body is turned slightly in the mounts making the reticle appear slightly tilted or off horizontal and vertical.
Using a good gun vice that allows you to adjust your rifle’s position and a set of scope mount levels can be the key to keeping the reticle in your scope aligned with the bore of the rifle.
Preparing to Adjust a Rifle Scope
Before you grab your rifle, ammunition, and targets to head to the range, it is important that you are properly prepared and have prepared your rifle. A little pre-thought about the process can save frustration and multiple trips to the range.
These are the things I encourage my students to include in the pre-range planning:
Bore Sighting is Critical
The first step in zeroing a rifle for me is to foresight the rifle and optic using a laser bore sighter. These are relatively inexpensive tools that can usually be used with different calibers of rifles without problems.
In essence, the bore sighter slips into the muzzle of your rifle and projects a laser downrange that is parallel with the rifle bore. I start with adjusting my scope to have a POA and POI at 25-yards. This ensures I don’t have to spend a lot of time just trying to get the rifle to strike the target when I start at the range.
Bore fighters are available in different styles. Some slip into the muzzle of your rifle, and others fit into the barrel chamber. Both styles work well and are relatively inexpensive tools to add to your range bag.
Selecting the right target to use when making rifle scope adjustments is important. The right target can provide you with a wealth of information about how to adjust a rifle optic to find the zero point.
Good targets have a grid system printed on the target face that is graduated in inches or half-inches. These grid marks give an instant visual cue for how much correction is needed to adjust a rifle scope.
Binoculars or a Spotting Scope
If you are sighting in a rifle scope at longer distances of 100 or 200-yards, a pair of binoculars or a spotting optic can make your day much more enjoyable.
A quick glance through your binoculars can tell you where your last shot printed on the target. This is much better than waiting for the range master to clear the firing line and allow you to make that long trudge downrange just to look at your target.
Take the Proper Adjustment Tools
Most modern scopes have adjustment knobs that are easy to grasp and turn. However, some scopes still require a screwdriver or some other specialized tool to make the fine adjustments or to set the re-zero options on the turrets. Make sure you have all the tools you need at the range to finish your scope adjustment project.
The Scope Adjustment Process
Once at the range, you should have all of your equipment, targets, ammunition, and your scoped rifle ready to start zeroing your optic and rifle. There are still a few things to do before you actually start firing rounds downrange.
Where do you Start?
On a new scope install, I always start at 25 yards and put at least three rounds on the target. If I have bore-sighted my rifle before coming to the range, most rifles will put those first rounds fairly close to the bullseye on the target. The actual difference between my POA and the POI gives me a good idea about what adjustments I need to make further downrange.
From there, you can move out steadily to your goal range, making small corrections along the way. I typically move out to 50-yards, then 100-yards, and if necessary, to 200-yards. An incremental process helps keep your optics adjustments small at each stage, which is a much easier process.
Making the Adjustments
You will probably find that you need to make both windage adjustments and elevation adjustments as you work through the zeroing process. Remember that methodical is the keyword here.
I see many novice rifle shooters making adjustments in a haphazard fashion. One problem I often see is shooters who adjust both windage and elevation at the same time. My advice is only to make an adjustment to one setting at a time.
I like to work on my windage adjustment first. I make small adjustments to bring the rifle and scope to the center horizontal line on my target.
Then, as I begin to adjust the elevation, I can watch for any deviation in the windage POI from the last shot. If the windage adjustment starts to move offline, it is a good indication that your reticle is not properly aligned with the bore of the rifle.
Don’t be alarmed if you see minor variations in the windage as you adjust elevation. Small differences in cartridges can account for some of this, as can variable wind conditions downrange. If you are shooting from a sled or gun vice, the number of variations should be slight, but may be noticeable.
A Note About Magnification Adjustments
It is my habit to zero my variable magnification scopes with the magnification adjustment to the middle of the magnification range. I do not advise changing the scope magnification setting during your zeroing process.
Once I am satisfied that my POA and POI are satisfactory at my chosen different, then I will adjust the magnification and shoot some additional test rounds. I have found some adjustable power scopes that will alter the POI slightly along the magnification power range of the optic.
Is Parallax Adjustment Advisable When Adjusting a Scope?
In my opinion, yes. An adjustable parallax scope keeps the target image and the reticle image in the same focal plane so that the images of both are crisp and clear. You want the best view of your target possible when sighting in your rifle and optic, so setting the parallax adjustment to the proper distance can be important.
Is The Process Different for First Focal Plane or Second Focal Plane Scopes?
There should be little if any difference in sighting in a first focal plane scope and a second focal plane scope. The major difference between these two types of scopes is where the reticle image is projected into the optic image. This should not, under normal circumstances, affect how you adjust your scope.
There is a lot of debate about whether the first or second focal plane scopes are better or worse. For me, the big difference is in range estimation and using scopes with built-in mil-dot or MOA markings on the reticle. It is, as far as I can tell, purely a personal preference for the shooter. You must decide if FFP scopes or SFP scopes are the best for you.
A few words about MOA and Mils
Before you start to adjust your rifle scope, it is important to know and understand how your rifle optic is graduated and makes adjustments. There are two popular measurement calibrations used in modern scopes. Many scopes are graduated in MOA or Minute of Angle. the other popular measurement is in Mils. Both are measurements of angles and are significant in choosing and adjusting your scope.
Without a long and detailed discussion about MOA and Mils, suffice it to say that it is the amount of adjustment you have on your optics that is the critical factor. High-quality scopes often are graduated in MOA.
The important thing to remember is that at 100 yards, each MOA moves the POI one inch. So if your scope adjusts one-quarter MOA per click on the turret it will move the POI by one-quarter inch.
A Mil graduated scope is measured in mil radians, another angular measurement. If you make a one-click adjustment on a Mil-dot optic, the POI at one hundred yards will move approximately 3.6 inches. A scope that makes 1/4 MIL changes per click will move the POI about three-quarters of an inch.
Mounting and Adjusting Your New Rifle Scope
For me, there isn’t anything much more enjoyable than mounting and adjusting a new rifle scope.
It doesn’t matter which particular scope you choose, putting that optic on your rifle and punching holes in those first few targets is an enjoyable experience. Knowing that the rifle and optic work together to put your bullet strikes on target where you want them is a huge satisfaction.