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Way back when I got to the end of my very first AR-15 project, I remember taking the upper to the local “gunsmith” for final assembly. While there, I also asked him to mount and “zero” my scope at the same time.
It seemed like a bit of voodoo at the time, as he mounted up my Trijicon TR-24, dropped a laser bore guide in the chamber, and then matched it up against a wall 15 yards or so away. Imagine my surprise when I took my shiny new rifle to the range only to find out that his hasty zero wasn’t much of a zero at all.
So there I was on my first range trip with a new rifle and optic, and having to figure things out as best I could. I’ve mounted and zeroed a lot of scopes since then, and I’d like to think I can explain it a little better than a lot of the other guides out there that assume a lot more experience. Sure, you could skip over this procedure go for a “bubba zero” and just kind of fumble around, but you will become a much better marksman by understanding your equipment and how to adjust it properly.
This procedure has a lot of overlap with obtaining a zero for your iron sights. I’ll be echoing some of the points made in my writeup on that topic as well.
It Starts With Mounting
Properly mounting a scope and getting everything torqued down to the right settings is another process all to itself. I’m going to leave that topic on the table today, as it really deserves a post all to itself. Needless to say, though, you really shouldn’t go too quick through this, any improperly tightened screws between the rings, the base, and even the mounting surface will make a repeatable rifle scope zero nearly impossible.
In the meantime, here’s a video from my friend Ilya Koshkin (the Dark Lord of Optics). He explains it really well and uses pretty much the same process I do.
The Rifle Scope
For this article, I’m basing my instructions off of a more traditional looking hunting or tactical scope. That said, the procedure is similar regardless of whether you’re zeroing a precision rifle scope or a red dot sight. The main piece of information you need to know is the adjustment interval for your scope or optic.
Most common optics use one of several increments for their zeroing procedures: 1/4 Minute of Angle (MOA), 1/3 MOA, 1/2 MOA, 1 MOA, and 0.1 Milliradian (MRAD).
Yes, I am aware that there are more than that, such as 1/8 MOA that is common amongst F-Class and Benchrest shooters. That’s besides the point. I only want you to understand that you need to know what the increment is for your optic.
Minutes of Angle and Milliradians
I put a much longer explanation of this in my post on Mils vs Minutes of Angle. So this is just the two-minute version to help you get oriented to angular measurement with riflescopes.
From here on out, you need to stop thinking about target impacts in terms of linear distance like “six inches low” and start thinking in terms of angular measurement. Linear distance doesn’t really help you in any way without also knowing the distance to the target.
Take, for example, the simple graphic of a circle below.
Imagine that you were at the center of the circle and firing along the dashed yellow line towards the perpendicular red line. If I told you that your point of impact was 43 inches left of your point of aim, how much adjustment do you need to make to your scope?
The answer is that you don’t have enough information, so you can’t. You would also either need to know the length of the dashed yellow line, your distance to target, or know the angle between the yellow line and your point of impact.
With many precision optics, you can simplify all of that down to just knowing the last point: the angle. Let’s touch on the two ways we measure this.
Minutes of Angle
In the circle example, I mentioned that you don’t know enough information to make an adjustment. The reason for that is that the linear distance between two points on an arc grows as the distance between the center of the circle and the edge of the circle grows.
Let’s use a single degree of angle for an example. If the angle between the two green lines was a single degree, then the red line would be two inches long at 10 feet of distance. But if we extend the range to 100 yards, the red line grows to five feet. At 1000 yards, it becomes 50 feet.
This is too coarse of a measurement for precision shooting, so we subdivide that single degree of angle in to 60 segments known as minutes of angle. A single minute of angle is 1.047″ at 100 yards, 10.47″ at 1000 yards. This is a much more manageable way to adjust sights, and is the most common increment for iron sights on battle rifles.
With precision optics, we often subdivide that single minute of angle into quarters, thirds, and halves. While technically these represent 15, 20, and 30 seconds of angle, we typically refer to them as 1/4, 1/3, and 1/2 MOA.
So that’s one way of measuring angle, and it’s the most common in the United States. But there is another that is also very common among military and precision shooters.
Milliradians
A milliradian is another way to measure angles and arcs. But rather than using degrees, we use another geometric aspect of circles called a radian. Merriam Webster defines a radian as follows:
A unit of plane angular measurement that is equal to the angle at the center of a circle subtended by an arc whose length equals the radius or approximately 57.3 degrees
Yeah, that definition didn’t make a lot of sense to me either, but I wasn’t an engineer and math wasn’t my forte. I included an animated graphic to help better illustrate what the definition is saying. The important part is not really what a radian is, but simply to understand that it is a consistent way to track angle.
In the definition, you probably noticed that a single radian is approximately 57.3 degrees, which is impossibly coarse for a precision rifle. That is why we subdivide a single radian into 1000 segments called milliradians (milli being the latin prefix for one thousandth). We often abbreviate milliradians as MRAD or simply “mils.”
If we divide 57.3 by 1000, we have 0.0573 degrees, which is roughly 3.43 Minutes of Angle. In real distance terms, that means a single MRAD works out to about 3.6 inches at 100 yards, making MOA a more precise measurement.
However, precision rifle scopes adjusted in milliradians typically work in 0.1 MRAD per click of adjustment, meaning that a single click (1/10th MRAD) is about 0.36 inches at 100 yards, just a bit over a single click of 0.26 inches for a 1/4 MOA optic.
Milliradians and the Metric System
I would be remiss if I didn’t touch on this rabbit hole a bit. I’ve been talking in terms of yards and inches so far so it might not be obvious to you yet, but milliradians work really well with the metric system because everything is divisible by 10.
Let’s switch from yards to meters for a moment. Since a meter is a bit longer than a yard (109 meters to 100 yards, roughly) the angle spreads a bit more. At 100 meters, a single MRAD covers 10 centimeters. That means that a single click of a 0.1 MRAD optic moves the impact by 1 centimeter.
At one thousand meters, a single MRAD equates to one meter, and a single click moves the impact by 10 centimeters. This makes math for calculating drop, ranging, and lot of other things a lot easier.
Because of this convenience, a lot of people assume that milliradians are part of the metric system. However, they are not. It’s just a happy circumstance of the divisible by 10 math.
For example, if we switch back to yards, the same holds true. One MRAD at 100 yards is 3.6 inches, which means it’s 36 inches at 1000 yards, or exactly three feet.
Angular measurements like this don’t care how you measure distance.
So, MOA or MRAD for You?
The simple answer here is to use what’s comfortable for you. All of my precision scopes are in MRAD, while all of my red dots and prismatic optics adjust in MOA. I have a whole different article dedicated to sussing out each of these systems and what makes them useful.
The bottom line is you should know what system your scope uses and then use it for your zeroing procedure.
Zeroing a weapon is not a training exercise, nor is it combat skills event. Zeroing is a maintenance procedure that is accomplished to place the weapon in operation, based on the Soldier’s skill, capabilities, tactical scenario, aiming device, and ammunition.
Its purpose is to achieve the desired relationship between the line of sight and the trajectory of the round at a known distance. The zeroing process ensures the Soldier, weapon, aiming device, and ammunition are performing as expected at a specific range to target with the least amount of induced errors.
The Rifle Scope Zero Procedure
With the math work out of the way, let’s talk about the process. I’m going to share one primary process for obtaining your rifle scope zero.
I am not going to give you the “one shot zero” trick or anything like that. Those are fine for what they are, but beginners are best served by executing the detailed process so they understand their equipment.
My process consists of the following steps:
- Select zero distance
- Set initial target
- Establish position
- Fire and adjust
- Confirm zero
Select Zero Distance
The right zero distance for you depends on a lot of factors such as how you plan to use the rifle, the optics you choose, and more. Many optics with bullet drop compensating reticles specifically call for a distance, such as 100 meters.
Hunters, or defensive shooters, typically use a point blank zero. This provides a margin of error above and below the point of aim and simplifies the aiming process.
Precision shooters often use a 100 yard or 100 meter zero so that they only ever dial their scopes down or use holdovers. Regardless, you need to select your desired zero distance ahead of time. I suggested spending some time with JBM ballistic calculator.
For our purposes today, I’m going to use a 77gr SMK launched at 2683 FPS and a desired zero distance of 100 yards with an MOA scope. This is my output from the calculator.
Set Initial Target
Most of the time, I like to set a my zero target at a closer range for an initial zero. Doing this at 25 yards typically rules out any wildly off shots that might not hit the paper at 100 or 200 yards. It also makes my final zero step a lot faster.
Zero Target Selection
So what do I use for a target? Just about anything will work. If you have a way to measure how far off your point of impact is, whether it’s with a ruler or the reticle of your optic, you can make correct adjustments.
That said, I generally like to use purpose-built targets. Rite in the Rain has some great weather-resistant ones set up for either MOA or MRAD optics.
If you don’t want to buy one of these targets, that’s fine. I’ve used just about everything including a blank paper plate. These targets just make determining your adjustments a lot easier.
Establish Your Position
To repeat myself from my article on zeroing iron sights, you should zero your scope from a shooting position you’re more likely to use. Many people zero their rifle scopes while seated at a bench and then actually use their rifle from prone, kneeling, or something else.
The problem here is that your zero can change from position to position, even if only a little. Obviously, there’s a balance to be had between stability and realism. When possible, I always try to zero from the prone or sitting position.
Whether you set up your position with a sling, bipod, bags, pack, or whatever, make sure it’s as stable and consistent as possible.
Fire and Adjust
This step happens multiple times. I much prefer to correct for elevation and windage separately from one another. Some people like to try and do both at the same time, but that puts a lot faith in the adjustment mechanisms to work perfectly well. You might expect that on an expensive precision rifle scope, but it’s not always true on less expensive optics.
Fire Five Shots
Aim at the center of the target and fire five shots. If you see your shots hit the paper, then that’s great, and keep going until you’ve fired all five. Do not try and correct your point of impact.
The goal is building data, and there’s a reason I like five shots as opposed to one shot or three shots. The more shots you fire, the more statistical data you have about your actual zero. The following image from TC3-22.9 illustrates the problem.
Were you to go off of only three shots, you might think the center of your group was in a very different location. Going up to five shots demonstrates that the one flyer was probably an outlier.
A single shot is even less useful than three shots.
Adjust Elevation
Once you’ve fired your first five shots, measure how much you need to adjust your rifle scope to bring your zero in line. If you’ve used the targets I linked to, this is really easy, as you just need to count the squares.
Alternatively, if you have a rifle scope with an MOA or MRAD reticle, you can measure the offset using that. Hold the vertical crosshair on the middle of the bullseye and then move the rifle up or down until the horizontal crosshair intersects the middle of the group. The distance you had to move the reticle is your adjustment.
Now that you know how much you need to adjust, dial that with your turret. Keep in mind which turret rotation direction moves the impact up or down. This is often different between different countries of origin.
Adjust Windage
Once again, aim for the center of the target and fire five more shots. If you did things correctly the first time, then your shots should be dead horizontal with the middle of the target.
Measure how much windage adjustment you need by either counting the squares or using your reticle. Make the adjustment with the turrets.
Confirm Initial Zero (Optional)
I’m marking this step as optional for two reasons. First, if your initial distance was the same as your final distance, such as using a zero at 25 or 30 yards, then you can go right to the next step.
Second, if you’re about to confirm at your final distance, then you might want to save your ammunition for that.
At this point, you may want to pre-dial any offset for your final zero. By that, I mean that you can adjust your elevation turret according to the known difference between your initial and final zero. Let’s look back at my original ballistic calculator output.
When zeroed at 100 yards, my ballistic calculator predicted that my point of impact would be 2.6 MOA low at 25 yards. Since we did our initial zero at 25 yards, then we can guess that we will have to add that much adjustment to get a final zero at 100 yards.
I figure that it saves a bit of time we we go ahead and add the required adjustment before the final confirmation zero. Keep in mind that you will rarely be able to match adjustments perfectly. With a standard 1/4 MOA-per-click turret, you would have to get “close enough” to 2.6 MOA of adjustment with either 2.5 or 2.75 MOA.
Confirm Final Zero
Your zero is not done until you’ve confirmed it at the desired distance. Now that you’ve gotten an initial zero, place a fresh target at the final distance of 100 yards (at least, in my example here).
Repeat the fire and adjust procedure from step four.
If you’re using the milliradian target, there is no easy conversion to go from 25 yards to 100 yards. But Rite in the Rain does sell a 100 meter sniper target suitable to the task.
Ideally, you wouldn’t have much (if any) adjustment to make here, and I’m usually more forgiving about firing only one group before adjusting elevation and windage.
At this last step, I like to finish whatever is left of my box of ammunition. Ideally, I’d get to fire 10 shots for a solid grouping, but if there’s only five left then so be it. In all, this whole zeroing process should have taken about 20 shots, give or take.
Bonus: Post-Session Cleanup
Even though this isn’t part of the scope zeroing process, I didn’t want to leave it out. Once you have your zero, I suggest a few important administrative actions.
- Set turrets back to zero: Don’t leave your scope turrets on the number they were when you reached zero. Most scopes allow you to loosen the turret cover and turn it so your new zero serves as the baseline. This makes it easy to return back to if you have to dial for any reason.
- If available, set zero stop: Not all scopes have this, but it’s a helpful thing to do for those that do. A zero stop serves as the new “floor” of the turret so that you have a physical reference point to return back to. If you get lost on your turrets during a match, you know you can always get back to zero by spinning the turret back down until it stops.
- Document your zero! Be sure to write down the rifle, scope, ammunition, and environmental conditions for when you set your zero.
Rifle Scope Zero FAQ
I thought it would be helpful to post a few questions I see pop up a lot about zeroing rifle scopes.
Boresighting typically means inserting a laser into the chamber on at the end of the muzzle. Without a laser, another common technique is to remove the bolt and set the rifle down in a way that you can peer down the bore and point it at a target downrange.
In either case, you would then align the scope to match the boresight. The reason I didn't use it here is that I really don't think it's necessary to do when you start with a closer target like 25 yards. It only adds extra steps and is rarely very accurate.
If you are only able to shoot your rifle at 100 yards due to range restrictions, then this is a good use case for boresighting (see previous question). The goal is simply to get "close enough" for a final zero confirmation at your desired distance.
If you are unable to obtain consistent groups, especially at 25 yards, then you either have poor shooting fundamentals or your scope is not mounted properly.
I suggest removing the optic and seeing if you still have a problem with iron sights. If the issue goes away, then it's likely the optic system.
Check the torque on all mounting surfaces including the scope base, ring bases, and ring clamps. Re-install the scope with correct torque and check again. If the problem persists, then it could be the optic itself.
The next step would be making sure the turrets are not loose. If they are solid, then it's likely time to use the warranty.
No, you do not need to start from mechanical zero. Many people think that starting at mechanical zero keeps everything in line with the bore, but there are too many factors in there. I have several high quality mounts that introduce a lot of windage into the system.
The only time I suggest trying a mechanical zero is when you are unable to hit paper at the 25 yard initial zero step.
In a quality scope, the point of impact does not change as magnification changes. If you are seeing this behavior, then it's time to have your scope repaired.
While my procedure here should use about 20 shots, which is a small price to pay for a solid zero in my opinion, it is possible to do it in fewer.
I've seen articles about getting a zero in as little as a single shot. I'm also going to disagree with them. Remember that the more shots you fire, the more data you have about your actual zero. A single shot doesn't give you enough data, and thus I don't think it should be used.
Always err on the side of more data.
Parting Shots
This concludes my brain dump on zeroing a rifle scope. I know this article is long and has lots of details. Many people are satisfied simply going to the range, setting up a target, and getting a quick zero for easy plinking. There’s nothing wrong with that.
I think there’s a lot of value in understanding how angular measurement works as it relates to ballistics and rifle scope zeroes. It builds confidence in your equipment and your capabilities with it.
One final thing: all of this doesn’t mean squat if you can’t effectively produce a group with your rifle. Too many people jump to blaming their rifle or equipment for bad groups, when the reality is their fundamentals weren’t up to the task. Establishing a high quality zero really comes after you learn to establish consistent groups.
Great read! Although I must point out that it’s 100 meters to the respective 109 yards not the other way around. Seems to self-correct right after that statement.