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Absolute vs Lower 1/3 Cowitness Sights

AR 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.

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.

 

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 cowitness sights that you can use.

On AR’s, the two most common cowitness types are – “absolute cowitness” and “lower 1/3 cowitness“.

 

Absolute vs Lower 1/3 Cowitness Explained

Difference Between Absolute vs. Lower 1/3 Cowitness

The graphic above shows the difference between absolute and lower 1/3 cowitness on AR’s with both optics and iron sights.

The way you control your type of co-witness is 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 cowitness – Optic is mounted at the same height as the iron sights or about 2.6″ above center of the bore
  • Lower 1/3 cowitness – optic is mounted slightly higher than the iron sights or about 2.8″ above center of the bore

There are advantages and disadvantages of each type of cowitness, which we break down in the chart below.

 

Absolute vs Lower 1/3 Cowitness Comparison Chart

Absolute vs Lower 1/3 Cowitness Comparison Chart

Type Mount Setup Pros Cons
Absolute Co-witness Optic mounted at same height as irons Consistency when switching between irons and optics. Closer to bore** Iron sights, may obstruct or clutter your sight picture
Lower 1/3 Co-witness Optic mounted higher than irons Extra height allows you to see over fixed sights (uncluttered view through red dot sight) Must raise and lower line of sight when switching between optics and irons (less consistency). Further from bore**

**The further your optic gets from the bore (center of barrel), the more difficult it is to sight-in correctly at a variety of distances (more variance between short-range and long-range point of impact). Luckily the difference between absolute and lower 1/3 setups is so minimal that’s barely noticeable. But it’s still worth mentioning.

 

US Army Service Manual AR 15 Ebook

 

Recommendations: Absolute vs Lower 1/3 Cowitness 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 absolute cowitness. 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 cowitness. 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 – cowitness doesn’t technically apply, but when choosing the mount for your red-dot sight, go with an absolute cowitness 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.

11 thoughts on “Absolute vs Lower 1/3 Cowitness Sights

  1. Good day good info I put your AT3 red dot on a Ruger 556 (absolute ) works great want to put one on an early mini-14 what would your advice be for a mount? thanks

  2. Hey Hugh, I would recommend running it without a riser on the mini-14, that’s how most people tend to run red dots on those. If you have any more questions, let us know!

  3. Thank you for a easy to understand, but fully informative article. Sound advice!

  4. Thank you for such a clear definition of
    co-witness, which would you recommend for use on a flat top using HK iron sights?

  5. Good Article, and well written for the AR Newbie and those considering eith a Red Dot or Iron Sights. The diagrams you supplied gave a good visual representation as well. Having the Pros and Cons of each type of system is a big help.

  6. What would the formula be for a carbine with an a2 carry handle?

    1. Buy a at handle mount for the red dot, cheek weld probably wont be much if its mounted lower 1/3.

  7. I am running into an issue where unless I use a riser on my red dot my iron sights co-witness in the top 2/3 of the scope. I’ve seen this with a few different red dots. And I cannot find a 1/4″ riser that will get me into an absolute co-witness.

  8. If you have fold down BUIS, go with absolute.

  9. Thank you for your wisdom and clarity on absolute,.

  10. Thank you for your valuable information on this topic. I own a Smith & Wesson M&P 15 Sport II, and the front sight is not a flip-up one, but a fixed one. Only the rear sight is a flip-up. So I think I should go with the lower 1/3 cowitness, in order not to clutter the view of the red dot…
    If I get it correctly, I should buy a Hi Profile 1″ Riser mount…. is it correct?
    Thank you!

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