You have two choices for lining up your AR-15 Iron Sights with your new favorite Red Dot or Holographic Sight: Absolute Co-witness or Lower 1/3 Co-witness. So, if you’re not sure how to set up these red dot sight configurations….and…you want the secret sauce for which co-witness to use? Follow along, we’ve got the answer.
Note: This article is focused on AR-15 setups that use red dot sights and backup irons, since this is the most popular configuration we see. But the concepts apply to any weapon where iron sights are used along with an optic.
Table of contents
Backup Iron Sights and Red Dot Sights
Red dot sights are one of the most popular sight options on modern weapons – offering both accuracy and speed of target acquisition. But like any battery-powered item, they can fail, so it’s wise to consider backup iron sights as added insurance.
Now, if you’re going to have two different sighting systems on your weapon, you’ll want to make sure they work harmoniously with each other. This is where “co-witnessing” comes into play.
What Are Co-witness Sights?
Simply put – co-witness refers to the alignment of your iron sights with your red dot sights. If your irons and your optics are both sighted in, you would expect them to be aligned (co-witnessed) with each other when you line up your shot.
This is the basic concept, but in reality, it’s a bit more complicated because there are different varieties of co-witness sights that you can use.
On an AR, the two most common co-witness types are – “Absolute Co-witness” and “Lower 1/3 Co-witness“.
Difference Between Absolute Co-witness and Lower 1/3 Co-witness?
The graphic above shows the difference between absolute and lower 1/3 co-witness on ARs with both optics and iron sights. If you are wondering where the best spot is to mount your red dot sight make sure to check out this article we put together to answer any questions you may have.
If you are looking for more information on adjusting your iron sights make sure to check out this FREE Official US Army Manual for AR15 / M4 / M16.
What Does “Absolute” Co-witness Mean?
This is the situation where your red dot optic and backup iron sights are mounted at the same height. If properly mounted the red dot should settle directly on top of the sight post and both the dot and sight post should be in the middle of the optic window.
What Does “Lower 1/3” Co-witness Mean?
This means that your red dot optic will be mounted higher than your iron sights. In this case, your iron sights will be in the lower 1/3 of your optic when you look at your dot in the middle of the optic window.
Control Your Type Of Co-Witness
This is all done with the height of your optic. Many red dot sights use riser mounts for this purpose – for example, the AT3 RD-50 PRO Red Dot Sight gives you a choice of mount heights.
- Absolute co-witness – Optic is mounted at the same height as the iron sights or about 2.6″ above the center of the bore
- Lower 1/3 co-witness – optic is mounted slightly higher than the iron sights or about 2.8″ above the center of the bore
There are advantages and disadvantages of each type of co-witness, which we break down in the chart below.
Absolute Vs Lower 1/3 Co-witness Sights Comparison Chart
Recommendations: Absolute Vs Lower 1/3 Co-witness Sights
So which setup is best for you? Keep in mind that either setup will work, so this really boils down to personal preference.
But we’re asked this question a lot, and this is what we recommend:
- If you have flip-up iron sights – go with an absolute co-witness. Since you’re probably going to have the sights flipped down most of the time, you might as well have your red dot at the “standard height”
- If you have fixed iron sights – we recommend lower 1/3 co-witness. This will give you an uncluttered view of the red dot, but you can still drop your line of sight to use the iron sights if needed.
- If you don’t have iron sights – co-witness doesn’t technically apply, but when choosing the mount for your red-dot sight, go with an absolute co-witness sight setup, because it will put the optic at the “standard height” that the AR-15 was designed for.
One Last Tip
If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.