How to Zero a Rifle Scope (MOA and Mil)

By80% Lowers

Before you set up your new rifle scope for long-range shooting and target plinking, you have to make sure that shiny, new optic is
zeroed. Today, we’re covering how to zero a rifle scope.

What is Zeroing?

When you buy
sights for your gun, you can’t just throw them on, aim and shoot, and
expect a bullseye. Zeroing means adjusting the sights so your point of
aim (POA) matches your weapon’s point of impact (POI) at a given
distance. In other words, the two points will be exactly the same.
Whether you’re zeroing a scope, red dot sight, or iron sight, the
process is the same.

How does it work?

You
need to first determine where rounds are impacting (POI) based on POA.
The best way to achieve this is by aiming at the center of a large paper
target at a known distance, pulling the trigger, and recording where
the round landed. If the round landed low and left of where you aimed,
you need to adjust the sights lower and left. This adjusts the point of
aim down and left to match the impact of the bullet. Basically, you want
the reticle to wind up on the exact spot where your round landed in the
first place. The process is more complicated than this, but we’re going
to walk through each step with visual aids.

Example

Reticles
use angular measurements to calculate the difference between POA and
POI. As distance increases, adjusting POA will make a greater difference
in POI than if the same adjustment is made at a closer distance. As an
example, if you adjust your reticle so point of aim shifts, say 1″ left
at 100 yards, then it will also shift left 10″ at 1,000 yards. A good
way to visualize how this works is to imagine yourself at a shooting
position inside a large circle that runs over you, behind you, and in
front of you.

The
size of the circle is determined by the distance to the target. POA is
the red line. POI is the orange line. If we measure the width of the
angle created by these two lines, we get the distance between the point
of aim and point of the bullet’s impact. As distance to the target
increases (as the circle gets larger), the angle’s width increases
proportionately. In our example, our target was 100 yards away, and
there was a 2″ difference between POA and POI. If we increase the
distance to our target from 100 yards to 300 yards, but make no
adjustments to our sights, the distance between POA and POI increases
from 2″ to 6″. That’s how much our angle’s width increases.

Real-world
factors like bullet drop, elevation, and wind will affect this angle.
But this is the mathematical way a reticle measures bullet impact
against aim. This is also why it’s important to zero your scope based at
a known distance: the reticle’s point of aim is adjusted with fixed
increments (0.25″ per click at 100 yards, for example), so you won’t
know how many clicks to make on your reticle unless you know the
distance to your target.

Types of Reticles and Turrets

These MRAD turrets provides 0.1 mils of adjustment per click.

So,
how do we actually measure these angular differences in point of aim
and impact if we know our distance to the target? We need a measuring
tool, and that tool can come in the form of the reticle itself. Your
scope’s reticle can measure the distance between POA and POI with either
a series of horizontal and vertical dots or lines, or a grid-like
pattern that overlays the target. These are all called subtensions, or
subtended reticles. The turrets are the exposed knobs on the body of the
scope ring, and they control the vertical (distance/elevation) and
horizontal position (windage) of the reticle.

Mil/MRAD (Milliradian)

Milliradians,
or simply mils or MRADs, divide our imaginary circles into 6,280 equal
parts. One mil equals 3.6″ of adjustment at 100 yards. If you enjoy the
metric system, 1 mil equals 1 centimeter at 100 meters, 2cm at 200
meters, and so on. If we used mils in our example above, we would need
to adjust POA about 0.5 mils up to close our 2″ gap to the bullet’s
impac

MOA (Minute of Angle)

Minute
of angle divides our circles into 21,600 equal parts. One MOA equals
1″ of adjustment at 100 yards. Conveniently, one MOA is also 0.25″ at 25
yards, 2″ at 200 yards, 3″ at 300 yards, and so on. In our example, we
would need to adjust our aim upward by 2 MOA to close our 2″ gap at 100
yards.

Which Reticle Should I Pick?

MOA
is the more popular reticle and turret combo for most shooters, simply
because it’s a lot easier to use. Calculating your ballistic data in mil
is more difficult if you’re used to the Imperial system of
measurements. Basically, if you’re American, you enjoy inches, feet, and
yards more than centimeters and meters (we do, too), and the mil system
is designed for calculating adjustments based on the metric system.

How to Zero a Rifle Scope

Now we
understand point of aim and point of impact, and how distance affects
both. We also know how to calculate the angular measurement between
these two numbers. Let’s see how to use the subtensions and turrets on
our scope together, so we can convert that angular measurement into
scope adjustment.

Adjusting the Turrets

All
scopes adjust the position of the reticle (POA) with turrets. Many
scopes have three: one for windage adjustment (left/right), one for
elevation and distance (up/down) and one for focus. You will only use
the first two turrets with the scope mount and to zero range, the latter
is for achieving clarity. Refer to your rifle scope instruction manual
to determine how many clicks of each turret is equal to one MOA or MRAD.
Most MOA turrets use 1/4-MOA adjustments, meaning each click moves
point of impact 0.25″ at 100 yards. Most MRAD turrets use 1/10-MRAD
adjustment, or 0.1″ at 100 meters.

MOA Reticle @ 100 Yards

This
scope’s reticle has one-MOA tick marks. Our round landed 3 MOA right
and 2 MOA high. At 100 yards, that’s an easy translation: We need to set
our scope adjustments 3″ right and 2″ up. On a quarter-click (four
clicks per MOA) turret, that translates into 12 clicks right and 8
clicks up.

MOA Reticle @ 25 Yards

At
25 yards, one MOA is 0.25″. The round landed about 5 MOA (1.25″) low
and 2 MOA (0.50″) left. With 0.25-MOA turrets, that translates into 20
clicks down and 8 clicks left to zero POA with POI

MRAD Reticle @ 100 meters

The
main difference you will notice between MRAD and MOA scopes is that
MRAD reticles have subtensions that look identical to MOA subtensions.
In this case, they’re called “mil dots.” Our round landed 4 mils right
and 2.5 mils low. At 100 meters that translates into 14.4″ rights and 9″
low. With 0.1-mil turrets, you would need to adjust right 160 clicks
and down 100 clicks.

MRAD Reticle @ 25 meters

Using
our mil dots to subtend, we see the round landed 4 mils left and 4 mils
high. At 25 meters, this translates into 3.6″ left and 3.6″ high. With
0.1-mil turrets, that translates into 40 clicks left and up to zero POA
with POI..

Zeroing Without a Reticle

Not
all scopes have mil dots or MOA subtensions, and iron sights and red
dots obviously don’t either. So, how do you zero your rifle or pistol’s
other, not-so-fancy gunsights? It all depends on the targets you’re
shooting at. In this case, we replace our subtensions and dots with
physical grid squares and markings on the target itself.

Depending
on how your iron sights or optics adjust (mils or MOA), you’ll need to
select a Rifle Sighting Target with either 1″ or 1cm grid squares.
Simply plant your target at a known distance again, likely 25 yards or
100 yards, and start getting rounds on target. Instead of using a
reticle to measure the distance between POA and POI, the grid squares on
the target measure for you. Aim center-mass, and figure out how many
grid squares off-center your round landed. Then you can calculate how
much you need to click your front or rear iron sights or red dot in the
appropriate up/down and left/right directions.

Zeroing by Bore Sight

If you’re
struggling to put rounds on paper or you don’t have a fancy reticle or
Sighting Targets, there is still a third way to get your POA and POI
matched up. Align the rifle scopes, optic, or gun sight with the bore
sight by literal sight.

Naked Eye Boresighting

How
does it work? Bore-sighting with the naked eye is easy: Pull the bolt
out of your rifle’s chamber and look through the receiver so you can see
through the rifle’s barrel and downrange. Align the barrel with a fixed
point of reference at a distance of about 25 to 50 yards. The smaller
and farther away the object, the better. Then you can align the optic
with that same object, which should bring POA close to POI. This will
not get you an effective zero, but it will help you get rounds on target
if your POA is way off.

Laser Boresight

Laser
bore sights can get an effective zero up to 100 yards away without ever
firing a live round. The laser boresight uses a pen- or
cartridge-shaped laser which sits inside the chamber or at the muzzle’s
opening. The laser replicates the point of impact of a live round with a
red or green beam, which provides a point of reference to align your
optic.

Boresighting is great because it doesn’t even require
calculations. You don’t need subtensions or grids on a target. Just
adjust the reticle until it matches the position of the laser beam, and
you’re ready to load a magazine and send some rounds downrange. You may
need to fine-tune your final zero after boresighting, because the
position of the laser can vary slightly from the exact position of the
bore.

The Best Distance to Zero


(Spoilers, it’s 25 yards)

Picking what distance to zero
your rifle at can be difficult because different distances affect the
overall arch of the bullet as it travels. The goal is to pick a zero
distance that affords the most “point-black” shooting across multiple
distances. That is, firing at a set distance will result in POA
perfectly (or almost perfectly) matching POI without any on-the-fly
adjustments.

By zeroing at 25 yards, the bullet trajectory for
most .22- and .30-caliber centerfire rifle cartridges remains relatively
flat for a substantial distance: Your rounds will typically land just
1.5″ to 2.5″ high at 100 yards, and POA will nearly match POI (less than
1″ difference) at 200 yards. This is a perfect bullet trajectory for
personal defense, close-quarters shooting, recreational range time, and
hunting. Most indoor and pistol shooting ranges are 25 yards, too. It’s
convenient to pick this zero because it can be used for all your long
guns and handguns.

Important Facts

Now you should have a basic understanding of why it’s important
to zero your rifle scope and other gunsights, and how it works. Here’s a
quick cheat sheet with the most important info:

  • Zeroing is adjusting point of aim (POA) so it matches point of impact (POI) at a known distance.
  • Two ballistic data systems are available: Minute of angle (MOA), and Milliradians (MRAD/mils).
  • MOA and MRADs/mils calculate POA vs. POI with equidistant reticle marks called subtensions.
  • 1 minute of angle subtension equals 1″ at 100 yards, 2″ at 200 yards, and so on.
  • 1 mil subtension equals 1cm at 100 meters, 2cm at 200 meters yards, and so on.
  • Most MOA turrets provide 1/4-MOA adjustments.
  • Most Mil/MRAD turrets provide 0.1-mil adjustments.
  • The best (and easiest) distance to zero at is at 25 yards.
  • If your sights don’t have subtensions, buy Sighting Targets.
  • Targets come with either 1″ or 1cm grid squares for zeroing.

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