Source Credit to guns.com | by Frank Melloni
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The absolute co-witness allows for iron sight backup in the event of electronic failure and is easy to set up. (Photo: Frank Melloni)
Regardless of what optics you attach to your rifle, it’s always handy to have a back-up in the event of an electronic failure of the red dot – be it a malfunction or the battery dies. Having iron sights will permit co-witness and engagement of targets even if the red dot dies. Let’s take a closer look at co-witnessing and how it works.
WHAT IS CO-WITNESSING: 1/3 AND ABSOLUTE
Co-witnessing refers to a method of mounting iron sights in a manner that allow for them to align with the red dot’s point of aim. This is achieved through the optics lens in one of two ways — lower 1/3 co-witness or absolute co-witness.
Absolute co-witness means that your red dot will sit on the top of your front sight post when aligning your irons and looking through your red dot lens. Lower 1/3 co-witness will require a riser for your red dot and therefore means that the red dot in your lens sits above the front post of your iron sights and your iron sights will appears in the lower 1/3 of the optics lens. Now, there are advantages and disadvantages to both.
The lower 1/3 co-witness allows for a duplicate zero without all of the clutter, although it is cheek weld specific. (Photo: Frank Melloni)
With an absolute co-witness the advantage is that both iron sights and red dot have the same point of impact. The downside, however, is that your sight picture is cluttered with a rear sight, a front sight and a red dot, which could impede your field of view.
The lower 1/3 co-witness offers a broader field of view with less clutter in the top 2/3 of the red dot lens and allows you to have a more upright position when using the red dot, hence a higher cheek weld. If you transition to the irons, you will need to adjust your cheek weld to account for the lower mounting position of your irons.
BEAR WITNESS? CO-WITNESS
The Sig Romeo 4H co-witnessed with Magpul sights. (Photo: Frank Melloni)
These are just a few of the many things to take into consideration when choosing the setup that works best for you. Remember, this is not a one size fits all and there is no right or wrong. Your rifle setup should always be tailored around your intended use and your personal preferences, so have fun with it!