You’ve heard the expression “two is one and one is none,” of course.
This phrase, popular among preppers and survivalists, signifies that if it’s worth having one of anything, it’s definitely worth having a backup.
If you have one piece of absolutely mission-critical gear (no matter what it is) and you lose or break it, what then will you do?
Nothing drastic, if you have a spare – you’re set.
Well, this applies to the realm of firearms, too, specifically to sight systems. This post will break down the most relevant corollary, called co-witness or co-witnessing, and what it means to shooters, as well as why it matters if you intend to supplement your Glock sights with a red dot.
What Does Co-Witness Mean?
To keep things as simple as possible, the concept of co-witness basically means the use of iron sights as a backup (or a “second” witness, hence the name) to a primary optic – commonly a red dot sight, with respect to a handgun.
In a nutshell, co-witness gives you two potential points of reference when shooting a handgun that has them – the optic as well as the iron sights.
Now, the thing is, there is more than one “type” or co-witness, or configuration, if you will.
One, and the most straightforward to understand, is what we call absolute co-witness. You have absolute co-witness between your iron sights and red dot sight if both sights are in perfect line with each other.
That is to say, you would have absolute co-witness between your iron sights and red dot sight if, when you switched on the RDS, the dot fell right at the top of the front sight, in between the rear post.
Complicating this is the fact that there are other types of co-witness in addition to absolute co-witness.
A common configuration is “bottom third” co-witness, also known as “lower third” co-witness. If your iron sights offer lower third co-witness, it means that your iron sights will still be visible within/through the RDS, but will appear below the bottom half of the sight window.
You could still run the iron sights through the RDS, or use them as a backup if the battery on the red dot died, but in such a configuration, the iron sights are not intended to serve as your primary sight, and you’d need to make adjustments to use them rather than the reticle of the RDS.
Why Do We Have More Than One Type of Co-Witness?
Back in the day, when red dot sights were first introduced, they were not as reliable as they are today. Moreover, those who carried their pistols and rifles for duty were accustomed to shooting over iron sights, not through modern, battery-powered optics.
Therefore, absolute co-witness was a more popular configuration early on. It wasn’t until red dot sights evolved and improved that shooters began to trust them as a primary optic to the point that they were comfortable dropping the iron sights to the bottom of the sight window.
Is One Type of Co-Witness Better Than the Others?
In truth, what configuration of co-witness is best really depends on your preferences. There is an argument to be made for both absolute and lower-third co-witness.
With absolute co-witness, you don’t need to make any adjustments to shoot over either your RDS or your Glock sights. Since the sights and RDS both produce the same single POA (point of aim) you won’t need to make adjustments in aim to use one over the other.
At the same time, absolute co-witness does require you to obstruct part of the sight picture of your target with your Glock; the bottom of your target will be obstructed by the Glock’s sights, and by the gun itself.
Adding to that, lower-third co-witness enables you to keep a much clearer sight picture since you’ll be able to see the whole target, with your Glock sights at the bottom of the sight picture, beneath the target.
And, even so, your iron sights are still ready to spring into action if your RDS suddenly dies or you enter an area with ambient lighting so bright that it makes the red dot hard to use.
Ultimately, though, it comes down to what your preferences are and whether you’re more comfortable with absolute or lower-third co-witness. Both can be serviceable with appropriate training.
Here for Glock Sight Upgrades?
Interested in upgrading your Glock sights to a set of Glock night sights? Take a look at our Glock night sights via the previous link; they are easier to install, CNC-machined from steel and treated with a durable QPQ nitride finish, and available in two heights. The mid-height is perfect for bottom-of-window co-witness with most slide-mounted optics and the tall height provides easy lower-third co-witness with most slide-mounted optics and also offers good visibility over most suppressors.
If you have any questions about the Glock sights we sell or want to know more about co-witness, contact our customer service today.
