A quality set of iron sights will serve you well for a long time. All you really need to do is install them, zero them, and go shoot.
Yet so many people don’t go that far. These days, most people are in such a hurry to replace the basic irons with optics that they end up never zeroing their iron sights at all, if they even have a set. Everyone tells them that they need a red dot sight or scope or else they will be ineffective.
The problem is that cheap red dot sights or scopes are a bad investment. They simply aren’t as durable or useful as a good set of iron sights. I would much rather a new shooter buy a decent set of irons and use those until they can afford a quality optic.
Don’t get me wrong, I’m not saying that irons are “just as good as” a quality optic. Good optics provide a huge benefit over iron sights with regards to speed and capability. What I am saying is that irons still work well while you save towards a well-made optic.
This article is about finding and setting a solid zero for your iron sights, regardless of their type. The same thought process works for a simple set of lightweight fixed sights, folders, or adjustable carry handle sights.
Most articles on this topic only go so far as giving you the procedure, but they lack an explanation of why you’re doing the steps you’re doing. I want to give you that context.
If you want, you could skip my explanation and jump right to my zeroing procedure.
But a little extra information never hurt anyone, right? Before I get to the how-to, let’s lay out a foundation for angular measurements.
Iron Sights and Angular Measurement
It’s important to talk about angular measurements because not all iron sights are constructed the same. Each model moves the point of impact a different amount for each “click” of adjustment you move the sight.
The classic A2 sight, for example, moves the point of impact 1 Minute of Angle (MOA) for every click. The detachable A4 sight moves 1/2 Minute of Angle, “Half MOA,” for every click. Many optics work in 1/4 Minute of Angle, “Quarter MOA.”
Those numbers aren’t truly accurate. But I’ll get to that.
So what is a minute of angle, and why does it matter?
The Magical Minute of Angle
Most novices take their rifle to the range and fiddle with the iron sight adjustments until they end up at something resembling a zero. Most of the time, they do this based on linear measurement.
“Come up one inch and over two inches.”
I totally understand why they do it this way. It’s the easiest measurement system to relate to. But sights don’t actually work that way.
They work in angular measurement.
Think of a compass, the kind you use for land navigation
The compass has 360 hash marks around the bezel, each one corresponding to a single degree of angle. On a compass, the distance between hash mark and the next is pretty small. But you have to think in terms of distance.
Imagine you and a friend starting at the same point. You follow a line extending from the 270 degree mark and your friend follows a line extending from the 271 degree mark. By the time you both walk 100 yards, you’ll be about five feet apart.
Technically they would be 62.82 inches, or 5.235 feet, but five feet works well enough for our example.
That five-foot distance between one degree and the next degree at 100 yards is impossibly coarse for a marksman’s iron sight zero. But imagine going even further out. Those two lines would continue diverging until they were over 50 feet apart at 1000 yards. That will never do.
So rather than use a degree for our sights, we divide it into 60 segments. One sixtieth (1/60) of a degree is a minute of angle.
This much smaller Minute of Angle (MOA) equates to 1.047 inches at 100 yards. We’ll round that to 1 inch. Extending the imaginary lines out from 1/60th of a degree now means that the lines still diverge, but at a slower rate.
This single minute of angle is better, and really is good enough for government work, but we can go further if we need to.
Subdividing Minutes of Angle
We can divide that minute of angle into another 60 segments called seconds of angle. But that is far too fine an adjustment. If you had a sight that could adjust in single seconds of angle, it would take forever to dial even just a few MOA.
Here is a ballistic chart for Mk262 77gr ammunition as an example. Pay attention to column: Drop (MOA)
Since adjusting in single seconds of angle is impractical, we need a middle ground.
Most modern iron sights adjust in increments of Half-MOA and Quarter-MOA. If you do the math, that works out to 30 seconds of angle or 15 seconds of angle, respectively.
This helps greatly speed up the adjustment process.
If you compare columns 2 and 3 of the ballistic chart, you’ll notice that the deviation from the drop in inches grows way faster than the deviation in minutes of angle. That’s the beauty of working in angular measurement as opposed to linear.
As the distance grows, so does the amount of space covered by a given angle.
If a half-minute of angle covers about half an inch at 100 yards, then it covers two inches at 400 yards.
If your adjustments are in half MOA increments, then four clicks moves your point of impact 16 inches at 400 yards.
That’s a much easy way to handle your iron sight zero.
I would be remiss if I didn’t mention that there is another angular measurement system called Milliradians. You’ll often see this abbreviated as MRAD, or just “mils.” This system takes advantage of a different geometry system and is very common with precision shooting optics.
However, I can’t think of any iron sight that use this system. If you want to know more, read my thorough breakdown and comparison between MRAD and MOA.
Now that the math is out of the way, let’s talk about the sights themselves.
Below, you’ll see a chart of the most popular rear iron sights on the market. For each one, I’ve listed its adjustment amount for both elevation and windage.
Keep in mind that this is only an estimate.
The actual amount of movement per click of adjustment depends on the distance between the front and rear sight. The longer that distance the smaller the point of impact moves for each click of elevation or windage.
For example, the USGI adjustable rear sight found on the M16A4 and M4 has half MOA clicks.
Except not really.
They are about .5 MOA on a rifle length sight radius, but closer to .75 MOA with a shorter carbine sight radius.
For all sight adjustments, no matter the increment, each click delivers about 40% more movement for the shorter carbine length sight radius compared to a full-length rifle sight.
Each of these numbers is listed for a rifle length radius. For convenience, I’ve rounded them.
|BCM||Folding Battle Sight||N/A||.5 MOA|
|BCM||Folding Sight (Rear)||N/A||.5 MOA|
|Bobro||Lowrider||N/A||N/A (Set Screw)|
|Brownells||360 Flip Up||BDC||.5 MOA|
|Daniel Defense||Fixed Lightweight||N/A||.5 MOA|
|GG&G||Standard Backup||N/A||.5 MOA|
|KAC||Micro 300||N/A||.5 MOA|
|KAC||Micro 200-600||BDC||.5 MOA|
|Larue Tactical||LT 103 BUIS||N/A||.5 MOA|
|LMT||Folding BUIS||.5 MOA||.25 MOA|
|LMT||L8A||.5 MOA/BDC||.5 MOA|
|LWRC||Skirmish||1 MOA||.5 MOA|
|M1 Garand||Rear Sight||1 MOA/BDC||1 MOA|
|M14/M1A||Rear Sight||1 MOA/BDC||1 MOA|
|Magpul||MBUS PRO||N/A||.5 MOA|
|Magpul||MBUS PRO LR||BDC (generic)||.5 MOA|
|MATECH||USGI||BDC (M855)||.5 MOA|
|Midwest Ind||ERS||N/A||.5 MOA|
|Midwest Ind||SPLP||N/A||.5 MOA|
|Midwest Ind||CRS||N/A||.5 MOA|
|National Match||A2/A4 Rear Sight||.25 MOA||.5 MOA|
|Scalarworks||Peak Ultralight||N/A||.5 MOA|
|Troy||Folding BUIS||N/A||.5 MOA|
|USGI||A16A2 Rear Sight||1 MOA||.5 MOA|
|USGI||M4/M16A4 Rear Sight||.5 MOA/BDC||.5 MOA|
|USGI||M16A1 Rear Sight||N/A||.5 MOA|
|Wilson Combat||QD Folding Rear||N/A||.5 MOA|
You might notice that many of the rear sights have “N/A” for elevation. That means that the rear sight is not adjustable.
But that’s fine.
Something a lot of people don’t realize is you should zero for elevation using the front sight.
If your rear sight has an elevation adjustment, as with USGI sights, then you should zero it on a specific setting. I’ll get to that in the procedures portion.
You might have to do a little investigative work to figure out your front sight adjustment.
Look down at the front sight detents, count how adjustment points you see. For a rifle sight radius, as found on 20″ barrels, the numbers work out like this:
- 4 Detents = about 1.25 MOA per click (most modern sights)
- 5 Detents = about 1 MOA per click (M16A1 front sights)
The quick math on that is that one revolution of the front sight post is 5 MOA on a rifle length barrel. It will be more per click on a shorter sight radius.
There are some oddballs out there. My Ashley Performance front sight post actually has 10 detents, for a measurement of .5 MOA per click.
As far as achieving an iron sight zero, all front sights are fairly coarse. But we’ll have to make due with what we got.
The Slow Math
John Simpson, who I interviewed for a podcast episode, is famous for saying, “If I can’t show you the math, then it’s just an opinion.”
Just in case you really wanted to know this and impress your friends. You can determine the actual click value for iron sights like this:
AR-15 sight posts have 36 threads per inch (TPI). One full turn is 1/36″ of movement. There are four clicks per turn on an A2 post, so one click is 1/144″ of movement, which equals 0.00694″. I’ll round that to .007.
Feel free to divide that 1/36″ by however many detents your front sight has and call this X. Next, measure the distance between the front and rear sight, and call this R.
To find the MOA of sight change distance X at sight radius R, use this:
That 3439 comes from the ratio of MOA to distance.
For illustrative purposes, I used a 20″ sight radius. But the math works for any sight radius you want to use for input.
And now you know.
Some newer folding front sights, like the Magpul MBUS PRO and KAC Micro have finger adjustable knobs. There isn’t a lot of data out there, but they seem to average 1 MOA per click.
The Ballistic Arc
One last thing before we get on to actually setting up our iron sight zero. Remember that bullets do not fly in a straight line. The rifle launches them in a ballistic arc.
Some people repeat a myth out there that bullets naturally rise after leaving the muzzle. They don’t.
Your sights are not level with each other. The rear sight is slightly taller than the front sight, which forces you to tilt the muzzle up ever so slightly when aiming. This provides the initial launch angle of the projectile.
Looking at this illustration, your zero is the point of intersection between the arc of the bullet and your line of sight.
Establishing an Iron Sight Zero for the AR-15
Now that you have a grasp of angular measurement and know the adjustment of your sights, we’re almost ready to get our iron sight zero. But first, there’s an important question a lot of new people ask…
How Often Should You Zero Your Rifle
I’m shocked at how many stories I hear of people showing up to training classes without their rifles zeroed. I don’t mean they were close at one point but fidgeted with something, either.
There are people who slap a set of sights or an optic on their gun and think, “Yep…that’ll do.”
Don’t be that guy.
As the TC says, zeroing is a maintenance procedure. As such, you should expect to do it periodically. The act of zeroing your rifle is aligning these six elements:
You’ve established a proper rifle zero when all six of those elements align to put the shot where it’s supposed to be. Once established, any change to any one of those elements requires another zero.
Swapping optcs or sights is an obvious reason to re-zero, but most people don’t think about the ballistic characteristics of one cartridge to the next. There might not be much at 25 yards, but 77gr SMK performs very differently than 55gr M193 at 500 yards.
Similarly, there is a difference between a bullet’s performance at sea level and at 8,000 ft elevation. That’s a change in the conditions that must be accounted for.
In short, most people should zero their rifles more often than they actually do.
Iron Sight Zero Procedure
First, lets bust some myths.
- You DO NOT need to set the sights to “mechanical center” prior to establishing an iron sight zero
- Zeroing at 25 yards/meters does not automatically give you a 300 yard/meter zero
- Bullets do not rise by themselves
- No, that crappy group is not “good enough for government work”
Ok, let’s get started.
Step 0: Choose the Right Distance
I’m including this step because it’s not technically part of the mechanical zeroing process, but it’s important nonetheless.
Most new shooters are satisfied with going to the range and picking an arbitrary distance to zero for. Most often this is 25, 50, or 100 yards. Now, there’s not really anything inherently wrong with those distances, but the better distance to zero for is your maximum point blank zero.
I’ve got a whole article on point blank zeroes, so definitely give that a read, but I’ll give you the short version here.
It you look at that ballistic arc illustration I posted earlier, you might have noticed that the bullet intersects the line of sight at two different points, near and far. The first occurs as the bullet is traveling upwards and the second as it’s falling downward.
You can use this behavior to your advantage.
A point blank zero, often called a battlesight zero (BZO), gives you that “set and forget” behavior whereby you hold the point of aim at the same position and know that the actual impact will occur a few inches above or below that point out to a certain distance.
Here’s another illustration from my article on bullet velocity and trajectory.
So the first step is to figure out your desired point blank zero based on your rifle and desired spread. If you don’t know these things yet, then that’s ok. The most common distances for this are 50 meters and 25 meters.
Step 1: Set Your Target
The new US Army 25 meter zero target is my preference. At 25 meters, each square is 1 MOA wide and tall.
That makes it easy to work your sight adjustments.
The middle white diamond is 4 MOA wide, which is the expected accuracy standard for Army shooters. There are rings on the inside set at 6, 8, and 12 MOA.
The black of the target is 16 MOA at 25 meters. That’s convenient because it’s 4 MOA at 100 meters. That means you can easily get a close iron sight zero at 25 meters and move the target back to 100 for confirmation with the same accuracy standard.
Also, at 100 meters, each square represents a quarter MOA, which lines up well with adjustments in a lot of modern optics. Unless you’re using MRAD, but that’s a different story.
The image I have here is not to scale, so I wouldn’t try to print it and use it for zeroing. It’s for illustration only.
Rite in the Rain happens to make a really nice version of this target in their weather-resistant paper. It also includes instructions on the backside for adjusting to different ranges and ammunition.
Amazon sells them in packs of 100. It’s worth checking out and keeping a stash handy. They also have the older targets as well.
If you’re keeping this barebones, then any target will do. I’ve used a paper plate with a dot in the middle. It just takes a little more work to do the measurements.
I always start with setting the target a 25 meters. The chances of missing the paper completely are smaller since it’s so much closer. Even if it’s on the edge of the paper, it’s still on the paper. I can work with that.
Step 2: Load the Rifle
This sound obvious, and it is. But keep in mind that your zero is a combination of rifle, shooter, distance, and ammunition.
I see this a lot in training courses. Someone shows up with a rifle zeroed with expensive 77gr match defensive ammunition, but wants to run the course with cheap surplus ammo.
The ballistic arcs of these cartridges are different, and they will not share the same zero.
Use the ammunition you plan on actually using, not a substitute.
If you insist on using one loading for “work” and another for practice, then keep track of the difference in sight adjustment. Lothaen at The New Rifleman actually has a good system where he puts a dot of colored nail polish on the sight drum to represent different loads. Note that doing that eliminates the usefulness of a BDC sight.
Step 3: Establish Your Position
90% of the time, when I got to the range and see other folks sighting in their rifles, they are sitting on a bench with the rifle in a rest.
Don’t be that guy. Unless, of course, you’re actually preparing for bench rest competition.
Remember that the zero is a combination of the shooter, the rifle, and the conditions. A huge component of that is the position used when zeroing the sights.
I recall an EIC match I shot while on active duty. For those matches, you don’t bring your own rifle. They handed me an M16A2 right off the rack. When we did our initial sight in, I placed the rifle’s handguard on a solid block to get stability. The groups were great, and I quickly got my zero.
But when the actual match started, my shots were going low. They were great groups, but just a few MOA below where I wanted them.
It turns out that the block I rested the rifle on affected my zero. I still won a medal in that match, but one of my lessons learned was to always zero the rifle from the position I intended to fire it.
I use the prone position most of the time for zeroing, but have also used the crossed ankle sitting position if space was limited. Both positions work well, as illustrated by two of my targets here from each position at 25 yards.
Once in your chosen position, really take the time to establish your natural point of aim. This guarantees the highest level of accuracy.
Step 4 (Optional): Set rear sight elevation to baseline
I already mentioned that you don’t have to set your sights to mechanical zero to start this process, and that’s true. But if your iron sights have some kind of BDC on them, like the carry handle, Matech, KAC Micro, or Magpul MBUS PRO LR, then you should place them on a specific setting first.
For the carry handle sight, that means using the “Z” notch on a 20″ rifle (or one click below if using M855).
If you’re using using carbine length sights and a carry handle, put the drum on the 3/6 marking. Remember that we have to account for the shorter radius between the front and rear sights on a carbine.
Check out my article on Revised Improved Battlesight Zero for more information about using the elevation drum on the carry handle sight.
For the other sights, check the instructions. If they don’t have a “zero” setting, then there is usually some other position you set to. The Magpul MBUS PRO LR, for example, tells you to set the sight to 200 and then zero it at 50 meters.
If your rear sight is not adjustable, then ignore this step.
Step 5: Fire Five Rounds and Adjust
Some people like to use only three rounds for this. I’ve even seen people sight in with a single shot, but that’s a very different technique more applicable to optics than iron sights. In any case, I always like to get some practice on my fundamentals.
I prefer five shot sighters because it increases my statistical data points. With five shots, I get a better average and any flyers are more easily discount
Make no mistake, fundamentals matter here. If your shots are all over the place, then you will have a lot of difficulties determining exactly how to adjust your sights. You need nice tight little clusters of shots.
Some people might fire one cluster, measure both elevation and windage, and then make both corrections. I tend to split these into two separate steps, adjusting windage first and then elevation after firing a second group.
If you’ve never adjusted the front sight before, there are plenty of tools out there that make the job easier. I’m constantly losing them, so I usually use whatever multitool or bullet tip that I’ve got laying around. The front sight post has an arrow indicating the direction spin it to raise the point of impact.
Step 6: Confirm Iron Sight Zero
The last step is confirming the iron sight zero. Once your shots are all within the desired point of impact, then you’re just about done.
Unless you want to use it at a distance other than 25 meters.
Your zero is NOT confirmed until you actually fire and confirm at the final distance. It’s a common mistake to zero at 25 meters or 50 meters and assume that you’re also good to go at 300 or 200 meters, respectively.
But that’s wrong.
The 50/200 and similar type zeroes are a myth. If you get an iron sight zero at 50 meters, then you zeroed only for 50 meters. If you want to be zeroed for 200 meters, then you need to put your target out at 200 yards and finalize your zero.
A Note On Windage
John Buol Jr. at Army Reserve Marksman points out that you need to be mindful of the wind when confirming your zero.
Most people zero their sights for a baseline, and then compensate for any changes.
Over to You
So there you have it, all the information you need to master your iron sight zero.
Does your process look any different?