A Guide to Co-Witness Red Dot Sights

Thirty years ago, optics were still somewhat untrusted on rifles meant for serious use. The prevailing attitude at the time was that optics fail, but iron sights don’t. Fast forward to the early-2000s: optics were being used in combat because of their obvious advantages. Rather than having to line up a front sight, rear sight, and a target in one’s line of sight, simply superimpose the dot on the target and fire.

Red-dot optics have come a long way since the 90s and early 2000s. Top name brands like Aimpoint, EOTech, and Trijicon have proven themselves reliable and robust, over and over again, across multiple theaters. They are rugged and dependable, and while optics gained wide acceptance during two decades of combat, they still haven’t become as fully trusted as iron sights. No matter how durable an optic is, it still has the limitation known as “battery life.” Irons are still perceived as more reliable than optics because irons don’t burn out, their batteries don’t die, and they don’t fog up.

One solution to the problem of failed optics is co-witness sights. Let’s take a look at the concept of co-witnessing.

What are Co-Witness Sights?

Co-witness sights are sights that can be seen (“witnessed”) through the optic, and simultaneously with its aiming point. If the optic battery dies, the user doesn’t have to remove it, tilt the gun, or perform any other maneuver other than shift the focal plane to the iron sights. Irons and red dot sights can be co-witnessed on rifles and pistols. The author was first introduced to the concept in 2004 while using an EOTech and back-up iron sights on his M4’s picatinny rail in Iraq, and it is fast and effective. The concept is so popular now that the acronym BUIS is universally recognized as “Back Up Iron Sights.”

Of course, co-witnessing only works with certain types of optics. You can only co-witness with zero-magnification (aka “1x” optics). Magnified optics distort the sight picture too much – life-sized sights mated to a 3x-magnified field of view doesn’t work out too well. This limitation is a slight downside to co-witnessing when using a rifle.

Co-witnessing also relies on optics and iron sights being roughly the same height above bore. Co-witnessed sights also don’t typically work on rifles with optics that are too tall. If the optic is too tall, the sights won’t line up with the optic. Some optics have mounting systems that permit the sights to be viewed below the optic. This is fast, but this isn’t really co-witnessing. On pistols, most optics interrupt the sight line for standard-height iron sights. To co-witness a pistol red dot typically requires sights that are taller than normal.

One other slight downside to co-witnessed optics and irons is field of view. The view through the optic can seem a little busy or cluttered. Putting both irons sights and an optic can also limit your field of view. Being able to see what is going on in front of you is critical to situational awareness. Despite its minor downsides, co-witnessing irons and optics has a lot of merit when feasible.

There are a couple of problems that co-witnessing won’t solve for you. If your optic obscures the sight line for some reason – if it fogs over, gets covered in mud, distorted by extreme heat, or the glass spider-webs – you won’t be able to see the irons. These are extreme outlier scenarios, but we want to be completely forthcoming.

Co-Witness Sight Types Explained

Optics that sit close to the same height-over-bore are prime candidates for co-witnessing. There are two types of co-witness that you should be aware of.

The first is the “lower third” co-witness. This means that the iron sights live in the lower 1/3 of the optic’s window. This has the benefit of improving your field of view by lowering the height of the sights in the optic. This also has the slight disadvantage of creating two sight pictures: the optics, and that created by the sights. It is a very minor difference, and is acceptable if the intent of the irons is only to serve as a backup.

The other is the “absolute” or “true” co-witness. This means that the line of sight for both the iron sights and the optic are exactly the same. This type of co-witness has some outstanding virtues. Zeroing is easier, and if the optic dies no shift is necessary at all – simply refocus on your iron sights and you are back in business.

Why should you use Co-Witness Sights?

There are a few reasons you might wish to use a co-witness system of both iron sights and a red dot optic.

The first is as a fail-safe backup in the event the optic breaks, in extremis. Though optics are more dependable than ever, they can still fail. Optics using the 2032 coin-style battery are infamous for loosening contacts and a resulting absent red dot. Red-dot optics are typically preferred on close-quarters weapons. In close quarters, speed is extremely important, and being able to instantly transfer the focal plane from one sight picture to another and get back in the fight is a massive advantage.

Another good reason for co-witness irons and optics is to learn to transition from irons to optics. Many pistol shooters with a couple of decades on iron sights have a hard time transitioning to red dot pistol optics. They are often seen on the range slightly rotating the gun in the classic “trying to find the dot” mode. Co-witnessed sights can allow the shooter to mount a red dot optic and use irons to smooth the transition, and as a backup on carry guns until that transition has occurred.

Finally, some shooters may prefer irons and optics for different purposes. On pistols, for instance, red dot optics have gained a reputation for being exceptionally well-suited for longer-distance (25-yard and further) targets, while irons are still preferred by many for close-up work. Alternatively, iron sights and optics may be preferred for different lighting conditions. Red dots without an ambient light sensor may be too dim to be visible during daylight, but if the optical sight is co-witnessed irons are right there, ready to go.

Co-witnessed optics and irons allow the shooter to have both instantly available, making his or her carry or competition gun that much more versatile. It can truly be the best of both worlds without having to over-specialize the weapon.

Steps to setting up your Co-Witness Sights

Setting up your co-witness sights isn’t that difficult. The technique you use will depend on whether or not the iron sights can be easily removed or flipped down without requiring the removal of the red dot. When possible, it is a good idea to zero each sighting system independently. That’s not always possible, so here’s what we recommend.

Most importantly, you want to ensure the components – sights, optic, and mount – are compatible with each other. This may require some digging, but verify you are going to get the sight picture you want, whether lower-third co-witness or absolute co-witness.

If using a system permitting field-removal of the irons sights, mount up your optic. Get a rough zero by correlating the red dot with the sight picture of the irons, then get rid of the irons, either by removing them or flipping them down. This allows you an unobstructed, uncluttered sight picture. It also permits you to avoid subconsciously looking at the sights while attempting to zero the optic and “chasing” the zero.

Now, zero the optic per the manufacturer’s recommendation. Though we aren’t getting too deep into zeroing, here’s a quick pro-tip: turn the optic to the lowest setting where the red dot is still visible. It will be as fine and obscure as little of the target as possible. Once the optic is zeroed, turn it off. Put the iron sights on, or flip them back up, depending on your system. If you remove them, re-zero them. If you simply flipped them down, confirm your zero. Once the irons are good, turn the optic on – you’re now good to go with a zeroed, co-witnessed sighting system.

If you are zeroing a pistol red dot, you probably won’t be able to take the irons off and put them back on without having to remove the optic. If that is the case with your pistol or rifle, zero the iron sights first, without the red dot in place. Once the irons are zeroed, mount the red dot and turn it on. You can get a head start by correlating the red dot with the sight picture of your irons. Now fine-tune the red dot, paying as little attention as possible to the iron sights.

Rely on XS Sights for all Your Firearm’s Sight Needs

When you’re in the market for sights, XS Sights is your go-to. We offer suppressor-height pistol sights that are perfect for co-witnessing with pistol red dots. We also sell sight installation tools so you can install our sights yourself, avoiding a time-consuming trip to a gunsmith. But that’s not all. Though XS sights has rapidly become known for innovative pistol sights like the “Big Dot,” we also manufacture a full line of rifle sights for ARs,AKs, and other tactical rifles, including flip-up backup irons and offset irons for those of you running magnified optics. XS Sights truly is a one-stop shop for all your firearm’s sight needs, whether pistol, rifle, shotgun – co-witnessed or not!