The What & the Why: Cowitnessing Sights

Both a red dot sight (RDS) and iron sights can often be installed on the same gun. One advantage of having both is that the iron sights can usually be cowitnessed with the RDS. And that can be done with a long gun or a handgun. The purpose is to facilitate a quick switch to the iron sights in case the RDS fails.

So what is a cowitness? If iron sights are installed on the same gun and can be seen through the window of the RDS, and the iron sights and the RDS aim the gun at the same point of impact (POI), then the sights are cowitnessed.

These are all red dot sights. Their internals may be a little different, but they all work in basically the same way. The Trijicon ACOG (top right) is a good optic but is magnified making it slightly different to use. (Doug Larson photo)

RDS have been around for decades. Probably a lot longer than you think. They have improved over the years and now are much smaller, creating a new category called miniature or even micro red dot sights (MRDS). The first RDSs were usually used on long guns, and have been installed on everything from rifles, to shotguns, to machine guns and other crew served weapons. MRDSs are so small now that they can and are used frequently on handguns.

And a note here. There is more than one type of RDS. Some are reflex sights and some are holographic sights, and some use a dot, or a chevron, or a triangle, or other figure or design as the reticle. And some are not red. For our purposes, we are not going to make a distinction between the operating internals, color, size of the device, or the reticle. They all work essentially the same from the user’s viewpoint, so we will refer to them all as RDSs.

This red dot sight is made by EOTECH and is a Holographic Weapon Sight which has internals that are a bit different than the internals of many other RDSs. The reticle is also different than many, but some shooters prefer it. (Doug Larson photo)

Back in 2014, I wrote a story for another publisher about the coming trend of using a RDS on handguns. At that time, I began to notice that more and more people were beginning to use them on defensive handguns, and even a few law enforcement agencies were beginning to recognize their usefulness on service pistols. I predicted that RDSs would become more common on handguns for law enforcement use, and they have. Of course, the general public has followed the trend.

But back then, they were fairly rare on handguns and it was hard to find a handgun that was set up for a RDS. I searched around and found a handful, even though competition shooters had been using them for years. Since then, RDS use on both defensive and competition handguns has grown dramatically and now several manufacturers produce handguns with a RDS installed or ready to accept one.

The US Military recently adopted a new sidearm, the M18. This P320 civilian version is equipped with a RDS. The iron sights on this gun are not high enough to effectively cowitness. (Doug Larson photo)

If a handgun comes with a RDS installed, the sights might be cowitnessed, or not. But if they are not, it’s easy to fix. First, the iron sights need to be high enough, or the RDS mounted low enough, that the iron sights can be seen through the window of the RDS. On an AR-15 for example, that is usually pretty easy because the iron sights sit fairly high above the centerline of the bore and when the RDS is installed, it is often at the right height. If not, a riser or mount of the correct height can be used.

But for a handgun, often the iron sights are set too low to be seen through the RDS window. But that can usually be fixed, too. All you have to do is replace the standard iron sights with iron sights that are higher than normal. These are sometimes called suppressor sights because they are designed to be high enough above a suppressor so that they can be seen for aiming over the suppressor. That same height often works for cowitnessing iron sights with a RDS.

Of course, the handgun’s RDS must be at the right height, and that is usually at the lowest height possible. Some RDSs come with different height mounts, so choose the one that is appropriate.

A RDS can also be used as an auxiliary optic for use with a scope. Sometimes they are mounted on top of the scope or offset at an angle to the side so that they can be used for quick shots at close targets. And that’s where RDSs really excel. They are great for fast engagement of relatively close targets. But a RDS can still be useful for targets that are a hundred yards or more away, depending on the precision needed and the size of the target.

This S&W M&P9 M2.0 comes from the factory with suppressor height sights installed. The top of the sights are high enough that they can be seen above a suppressor. Suppressor sights are usually high enough to cowitness with RDSs and are available for some guns. (Photo courtesy Smith & Wesson)

RDSs are usually not magnified. In other words, the magnification factor is 1X. And that is part of what makes the RDS so useful for fast, close work, because both of the shooter’s eyes can remain open and the target can be viewed using either eye. And it doesn’t matter which eye is dominant. Just bring the gun up and place the dot on the target. And the shooter’s focus can remain on the target. That’s all it takes to aim with a RDS. It is not necessary to line up the rear sight, the front sight and the target and then focus on the front sight. And unlike with a scope, which usually has some degree of magnification, closing one eye, using the dominant eye or training to overcome eye dominance is not critical.

When using a RDS, the iron sights are usually referred to as backup sights, or backup iron sights (BUIS). That’s because the RDS is used as the primary aiming device and the BUIS are there to be used in an emergency if the RDS fails. A RDS might break – it’s a mechanical device after all – or the power supply might run out. If the RDS and the BUIS are cowitnessed, then the BUIS can be immediately used to aim the gun because they are visible through the RDS’s window and are already zeroed at the same place as the RDS is zeroed.

Cowitnessing is actually pretty simple. If the BUIS are zeroed, the fastest way to do it is to look through the RDS and adjust the dot using the elevation and windage knobs or screws so that the dot, or whatever is the aiming point, sits right on top of the front sight when the BUIS are aligned. Of course, the gun should be test fired after adjustment to confirm that the POI and the point of aim (POA) for both the RDS and BUIS are the same.

The sight picture through a red dot sight with cowitnessed iron sights. This RDS/BUIS combination is on an AR-15. The rear sight is folded down out of the field of view. Since the iron sight is located in the center of the RDS, it is said to be an absolute cowitness. (Doug Larson photo)

If instead, the RDS is zeroed first, the BUIS can be adjusted so that the front sight is just below the dot. If neither is zeroed, then zero one and bring the other to the same POA as described above. Again, test fire to confirm the zero of both.

Although it is no more complicated than that, one thing to consider is where in the RDS window you want to see the BUIS when properly aligned. That depends largely on personal preference. Some shooters say that the front sight is a distraction when using the RDS and say it clutters up and interferes with the sight picture and viewing the target. For others, it makes no difference.

There are options if the front sight bothers the shooter. And these apply more to a long gun, especially an AR-style gun, than a handgun. That’s because there are more BUIS and RDS mount options for ARs. It has to do with how high in the RDS window the BUIS sits.

The front sight on this AR-style carbine can be folded down out of the line of sight. It’s the shooter’s choice and the owner of this AR leaves the front sight up for fast use in case the RDS fails. (Doug Larson photo)

By choosing a higher or lower RDS mount, or selecting higher or lower BUIS, the height of the BUIS in the window can be adjusted. For ARs and many other long guns, the mounting point for both the BUIS and RDS is a Picatinny or M1913 rail. And, depending on the RDS, there are several different height mounts or types available. There are also a wide variety of BUIS available for ARs. There are not as many variations in BUIS or RDSs that are available for handguns though.

Some experienced shooters and instructors like the BUIS located in the lower 1/3 of the RDS window. That’s called a 1/3 cowitness. Other people like them in the center of the window and that is called an absolute cowitness. Still others, as said earlier, don’t care. So if different heights are available, choose the height of the BUIS or the RDS that you want.

Another option on ARs and some other long guns, is to use folding BUIS. These are very common. With them, the BUIS can be folded down so they are out of the line of sight until they are needed. They are useless though until they are raised, which takes time. So some operators leave the sights up even though they can be folded down. The thought is that they then can be used quickly in an emergency.

Some shooters who use folding sights fold the rear sight down, but leave the front up. It’s kind of a compromise between folding both down and leaving both up. With the rear down and the front up, the window of the RDS is used as a sort of large rear aperture with the front sight centered in it. This serves as a rough rear sight that in coordination with the front sight will usually get a hit on target, especially at close range. Obviously though, precision shots more are difficult if not impossible.

If the target is farther away, there is usually more time to get the shot off. And there may be enough time to raise the rear sight so a more precise shot using the BUIS can be made.

This is a traditional AR front sight that cannot be folded down out of the line of sight. The RDS mounted on this AR (not visible in photo) is cowitnessed with the front iron sight which remains in the sight picture all the time. With training and practice, most shooters can get used to it. (Doug Larson photo)

I know that regular readers of The What & The Why are going to get tired of reading it, but again, it is important that you get good training from a reputable instructor or school on how to use a RDS. There are several schools including, but not limited to, Gunsite Academy and SIG Academy. Find one and get enrolled. Sure, it’s expensive, but it’s the kind of training that could save your life or the life of a loved one.

That’s the what and the why of it.

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About the author: Doug Larson is a former Contributing and Field Editor for Guns & Ammo magazine, Doug Larson’s articles have appeared in many top firearm publications. He has completed hundreds of hours of firearm and self-defense training provided by some of the finest world class gun fighting instructors and schools. He has experience with handguns, rifles, shotguns, submachine guns, machine guns and other crew served weapons. He reports on the tactics, techniques and procedures developed by real life gunfighters and taught at the best martial arts schools. This information is passed on to the reader to stimulate thought and a desire to get the best training possible.

{ 1 comment… add one }
  • TOM BROLLINI November 23, 2020, 11:46 pm

    I do that with all my ARs with fixed or flip ups. Also use red dot/holo that have a permanent black reticle that does not need battery & is always up & ready as well as elect sight. e.g. Burris AR-332 Red Dot Sight – 3x32mm

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