Tactical Skills for an Adventurous Life

The Complete Guide to Your Iron Sight Zero

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A quality set of standard sights will serve you well for a long time. All you have to do is get a good iron sight zero, and you’re set.

Most people are in such a hurry to replace the basic irons with some fancy optic that they end up disappointed. Everyone tells them that they need a red dot sight or scope or 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.

Classic carry handle iron sight from Bravo Company USA, which has 1/2 MOA adjustments for an iron sight zero
The classic “carry handle” rear sight

It’s a different story when you get into extremely tough and reliable combat-grade optics. Combat optics provide a huge benefit over iron sights with regards to speed and capability. But this article isn’t about zeroing those optics. It’s about a solid zero on the classic fixed iron sights, or even folding backup iron sights (BUIS).

Most articles walk you through the basic steps of getting your iron sights zeroed, but they lack an explanation of why you’re doing the steps you’re doing. 

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.

Angular Measurements and Your Iron Sight Zero

It’s important to talk about angular measurements because not all iron sights are constructed the same. Different sights have different amounts of adjustment for every “click.” 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, by the way. But I’ll get to that.

So what is a minute of angle, and why does it matter?

The Magical Minute of Angle

Rifle sights do not work based on an arbitrary linear measurement. Most novices take their rifle to the range and fiddle with the adjustments until they end up at something resembling an iron sight zero. They do this purely based on measuring inches on a piece of paper. 

“Come up one inch and over two inches.”

Those adjustments do not work in linear measurements, they work in angular measurement. 

Think of a compass, the kind you use for land navigation

Suunto MC-2 cmpass
 My Trusty Suunto MC-2

There are 360 degrees in a circle. The distance between one degree and the next on a compass is very small. But if you draw lines extending 100 yards from those two tick marks, they would be five feet away from each other by the time they reached 100 yards.

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.

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.

That 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.

The minute of angle chart useful for obtaining a zero
Chart from TC 3-22.9 Depicting Minute of Angle

This single minute of angle is better, but we can still go further.

Subdividing Minutes of Angle

Technically, we could further subdivide 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.

Use this dope chart from my article about point blank zeroes for example.

JBM ballistic table

In the third column, Drop (MOA), you see the angular adjustment needed for each range. If you had an iron sight that adjusted in single seconds of angle, you would have to click it sixty times for each minute of angle. For some of those drops, you would be cranking for a long time to achieve an iron sight zero.

So 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.

Those adjustments work for both elevation and windage. 

This system is convenient because of the angles involved. If you look over that 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 because the minute of angle continues to get wider as the distance increases.

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 of moves your point of impact 16 inches at 400 yards. That’s much more usable for an iron sight zero.

Milliradians

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 sights that use this system. If you want to know more, read my thorough breakdown and comparison between MRAD and MOA.

Sight Adjustments

Ashley Performance front sight post
Ashley Performance front sight post on my rifle built for iron sight usage

Now that the math is out of the way, let’s talk about the sights themselves. This is 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

Each of these numbers is listed for a rifle length radius. For convenience, I’ve rounded them.

Rear sights

ManufacturerModelElevationWindage
ARMS#40N/A.75 MOA
BCMFolding Battle SightN/A.5 MOA
BCMFolding Sight (Rear)N/A.5 MOA
BobroLowriderN/AN/A (Set Screw)
Brownells360 Flip UpBDC.5 MOA
Daniel DefenseFixed LightweightN/A.5 MOA
GG&GStandard BackupN/A.5 MOA
KACMicro 300N/A.5 MOA
KACMicro 200-600BDC.5 MOA
Larue TacticalLT 103 BUISN/A.5 MOA
LMTFolding BUIS.5 MOA.25 MOA
LMTL8A.5 MOA/BDC.5 MOA
LWRCSkirmish1 MOA.5 MOA
M1 GarandRear Sight1 MOA/BDC1 MOA
M14/M1ARear Sight1 MOA/BDC1 MOA
MagpulMBUSN/A.5 MOA
MagpulMBUS PRON/A.5 MOA
MagpulMBUS PRO LRBDC (generic).5 MOA
MATECHUSGIBDC (M855).5 MOA
Midwest IndERSN/A.5 MOA
Midwest IndSPLPN/A.5 MOA
Midwest IndCRSN/A.5 MOA
National MatchA2/A4 Rear Sight.25 MOA.5 MOA
ScalarworksPeak UltralightN/A.5 MOA
TroyFolding BUISN/A.5 MOA
USGIA16A2 Rear Sight1 MOA.5 MOA
USGIM4/M16A4 Rear Sight.5 MOA/BDC.5 MOA
USGIM16A1 Rear SightN/A.5 MOA
Wilson CombatQD Folding RearN/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.

All elevation changes for iron sight zero are made with 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 next portion.

Front Sights

Front sights are fairly standard. 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:

Ashley Performance front iron sight zero
Ashley Performance front sight with .5 MOA adjustment
  • 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

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 arctangents and other fancy math. Just hit the “I believe” button and go with it. 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.

There is a myth out there that bullets naturally rise after leaving the muzzle. This is wrong.

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.

A simple illustration of how your iron sight zero interacts with the curve of the bullet

Your rifle’s zero is an intersection point between your line of sight and the ballistic path of the projectile. This is very important to choosing the right zero for your rifle.

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

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. 

– US Army TC 3-22.9, Appendix E

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. It aligns these six elements:

  • Shooter
  • Weapon
  • Sight
  • Ammunition
  • Conditions
  • Distance

A rifle zero is established 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 optics 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 1: Set your target

When you zero your rifle, you need a target to shoot at. Really, any target will do, but some make this a lot easier than others.

The US Army zero target for iron sight zero
US Army Zero 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.

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.

.223 cartridges in front of AR-15
When establishing your iron sight zero, use the ammunition you actually plan to run in the gun when it matters

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 their zero will not be accurate. 

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 using carbine length sights, put it on the 3/6 marking. 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 discounted.

This image from TC 3-22.9 illustrates why I prefer five shot groups. The three shot group on the left makes it difficult to determine an average point of impact. The group on the right shows a better representation and lets me discount the flyer as an anomaly.

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.

Target results while establishing iron sight zero.
Groups 2 and 3 are usable for establishing zero. Group 1, however, doesn’t provide you with a lot of information. You can see that the whole group is off to the right a bit, so there is certainly some windage adjustment needed. But how much elevation is required? The group is too large to tell.

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.

Note that the front sight adjustment is pretty course at between 1.25 and 1.75 MOA. Don’t frustrate yourself by trying to get it perfect.

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.

The image here comes from my post on velocity and trajectory. It compares a 50-yard zero fired from three different barrel lengths. I used ballistic data for 55gr M193. Notice how the shot impacts disperse.

This diagram shows the impact displacement for a 50-yard zero. Notice that the 50 yard and 200 yard marks are NOT the same. They might be close, but close is not a zero.

Whatever you choose as your final confirmation zero distance is up to you. 

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.

When confirming zero at ranges past 100 meters, the effects of the wind needs to be considered and acted upon, if necessary. If a zero is confirmed at 300 meters on a windy day, and then the weapon is fired at a later date in different wind conditions or no wind at all, the impact will change.

– John Buol Jr.
Image from TC 3-22.9 regarding the effects of wind

Remember, the zero is a combination of factors that include the conditions. If you zero your rifle in a 10 mph crosswind, then that’s your zero. If the wind isn’t there the next day, then your conditions have changed.

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?

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