• Post author:
  • Post last modified:August 6, 2023

Zeroing a red dot sight for a shotgun is very different than for a rifle.

In this guide, let's learn how to zero a shotgun red dot sight that involves balancing among pellets spread, point of aim, and point of impact.

It's not practical to have only ONE zero that magically optimized for everything.

Pro shooters pick the right choke tube, ammo type for his/her particular length barrel shotgun, then collect shot data from various distances, and lastly zero the sight accordingly.

Let's learn more…

Check Out: Best Red Dot Sight for Shotgun

Why Use Red Dot Sight On Shotguns?

There are so many different applications whether it’s home defense, 3 gun, hunting, clay shooting, military, trap and skeet, and a lot of uses out there.

Mounting a reflex sight on a shotgun is a new concept in the past few years, and it has several advantages such as:

  • Fast target acquisition
  • Parallax free
  • Without aligning iron sights
  • Shoot both eyes open

The first thing I want to address is to get a recoil resistant sight otherwise, it will lose zero due to heavy recoil, and it will be pointless to mount it on a shotgun.

Products like the Trijicon RMR and Aimpoint Micro S1 are built to handle heavy recoil G Force.

How To Zero a Red Dot Sight On Shotgun For Buckshot & Slug

Please don’t expect all the pellets to hit literally the same spot where your dot was aiming, even with a slug is different, unlike centerfire rifles where you get 0.25” shot groups at 100 yards.

For shotguns, most people shoot up close, and you want to pay attention to is your choice of ammo, shot pattern and choke tube because they matter.

Here is a general rule of thumb!

Zero the dot to cover the MOST concentrated buckshot pattern after 3 shots.

For about a 6″ – 9” grouping at roughly 18 – 30 yards is a good zeroing distance before it spreads too much and becomes a problem. 

For Slugs

please use the same zero for the buckshot, and holdover just a few inches higher when shooting at targets at 50 or 100 yards.

  • Test each choke tube for the tightest grouping
  • Only zero for the most consistent ammo.
  • Always be cognizant of the distance you’re shooting at all time.

For an unchoked gun it will spread about one inch per yard with buckshot in your house. Each OO buckshot pellet is almost a size of a 9 MM pistol bullet.

So you want to know where those are going every time you pull the trigger to prevent bad things from happening.

Why Shotgun Pellet Pattern Matters

Before you get into zeroing your sight, I want to briefly talk about why shot pattern matters.

In 3 gun world, shotgun DOPE ( Data On Previous Engagement) is equally as important, but it’s not being talked about much.

When shooting competition, many people believe shotgun sprays pellets all over the place and there is no reason to perfect its accuracy.

That’s not necessarily the case for practical reasons. If you’re new you probably buy the cheapest birdshot to shoot on the range, and not know much about various pellet patterns with various different types of loads.

The purpose is to know exactly what the pattern is doing and have some control over how many of the pills are hitting any given target area, or know at what distance was starting to lose control the patterns.

How Choke Tube Affect The Shot Groups

So I went out and did some homework by getting some 12GA choke tubes and different types of target loads. Choke tubes have different thickness, and there are 4 types:

  • Cylinder Choke
  • Improved Cylinder
  • Modified Choke
  • Full Choke

It controls how quickly the wad will follow it from the shot column. After the wad flies out of the barrel it opens up and falls away, and that also the time the pellet starts to spray.

So the tightness of the choke tube will influence how quickly the wad will open up by giving it a final squeeze at that last moment before leaving the barrel.

Choke Tube Types Illustrations

Image referenced from aegisacademy.com

Can I Shoot a Slug with a Full Choke?

Many people concern about whether a slug can fit through the end funnel of a full choke.

Will it get lodged in there or blow up the barrel?

If a particular slug can fit through the choke, then it's okay to shoot if you have not tested it please don't shoot it.

Improved cylinder choke gives the best performance for shooting slugs because the choke gives the projectile a little more squeeze before leaving the barrel. A standard full choke with a standard lead slug is safe.

As you go down the line with a tighter choke, safety becomes an issue.

Test And Record Your Shotgun DOPE

Perfect Shot Pattern Group

Find an outdoor range that lets you shoot various shotgun shells because most indoor range only allows slugs.

Get a big sheet paper like this and start at 5 yards and then start walking back in 5-yard increments with every choke and various ammo.

Last, circle the shot pattern and document it for your own reference. If you’re shooting steel plates at a match, know your pattern grouping would help you shoot better at any particular distance.

Use The Data For 3 Gun Matches

3 Gun With VEPR 12

Sometimes in 3 gun match will have targets placed very close to each other, and if you know your distance and pattern, then you can hit on both by aiming at the middle.

Other times, there will be penalty targets on either side of a scoring target. You have to make sure all the pellets will pass right through without hitting anything else, or you might need to get closer to shoot for a reduced pattern.

Pick Your Choke Based on DOPE Data

Do you ever feel like you just randomly pick chokes without knowing what exactly it does? Here is a tip you can use.

After you have collected the DOPE from various distances and chokes, start to pick out areas on the paper that are the size of clay with no pellet hit at all.

Once you have that information, you can critically think about the shotgun stages you gonna shoot, and pick the right choke to use without guessing.

Shot Groups Expands At Further Distance

As you back up further and the pellets start to spread out even more to get a bigger pattern.

The first thing you will notice is that the shot pattern in the center is still more concentrated, and there are still pellets hitting around the outside.

If you’re hitting clays you know the pattern and you can hit them better, and it only takes one pellet to break it.

Random Shot Patterns Increase As Distance Increases

Shotgun Pattern Missing Clay

However, At some point, this continues to spread out and then the pellet pattern density becomes random, which means even with a good aim, you might still miss the target the size of a pigeon clay because there are no pellets hitting that spot.

A lot of people who don’t test their shot pattern on paper never know that this happening. So testing your shots on paper is a critical step in order to understand your setup.

Choke Tube On Longer Barrel

You have to do the DOPE collection again with different barrel lengths with various chokes and loads.

The velocity and burn rate will be different, and how the wad interacts with the choke on a longer barrel at a different time would be different as well.

Final Thoughts on Shotgun Zero

If you are using a shotgun for any serious purpose such as 3 gun or home defense. This is definitely the information you must have.

Red dot sight provides fast target acquisition, and it's very useful for shotgun applications even though it didn't seem like it. With a full understanding of how the shot pattern, choke tubes, shooting distances all work together, zeroing a red dot becomes easy and no more guessing.

Just remember!

Testing and collecting the shot group data for every ammo type, choke tube, and barrel length are very important.

Pick your favorite ammo and zero your dot based on that.