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AR-15 Sights: Fixed vs. Folding & How to Co-Witness

AR-15 Sights: Fixed vs. Folding & How to Co-Witness

Posted by 80-Lower.com on Aug 28th 2017

The world of AR-15s is flooded with optics and sights. Picking the right setup for your black rifle can get a little confusing. You want a nice red dot or other optic, but you still want the ability to hit targets with a traditional set of irons. In this guide, we're breaking down the differences between fixed and folding sights and how to properly co-witness your optic or red dot with the sights of your choice.

Fixed AR-15 Sights

We can’t lie when we say we actually prefer a fixed front sight, and many instructors and professional shooters do, too. The traditional A2 front sight has stayed popular because it’s dependable, easy to adjust, and it's tough as nails. Its position also allows for perfect co-witnessing with glass and optics, which we'll explain later. In fact, the A2 front sight post's original height is the standard that most other modern iron sights are now based on. To this day, the A2's sight picture has been the official sight picture and iron sight setup for the U.S. military's service rifles since Vietnam.

Much of the original M16A2's design has fallen out of favor: The full 20-inch barrel, the bulky fixed stock, a carry handle on the upper receiver, plastic handguards, and more. But that fixed front sight is still around because it works so well. But what about out back, where you're lining up your shots? Your choice in rear sights is more important because it poses a greater risk of interfering with your optic or red dot.

Picking a Fixed Rear Sight

Other than settling for an original A2 back-up rear iron sight, you may have trouble finding a solid, fixed rear sight that plays well with your red dot or optic. The Daniel Defense A1.5 is one of the better options out there because its compact and lightweight (1.7 ounces). Fixed rear sights typically offer finer adjustments and great accuracy. They also often come with separate peep sights for close- and long-range shooting. The downside to fixed rear sights is they typically get in the way of larger optics and they crowd the sight picture.

Folding Rear Sight Advantages

Folding rear sights have become the new hotness. AR-15s have become more accurate and capable of operating at greater distances. And with a flood of new patrol optics, magnifiers, red dots, and variable-power optics hitting the market, real estate on the upper receiver has shrunk considerably. For most shooters, an optic or red dot has replaced the iron sight as a primary method of target acquisition. That means you need an iron sight that doesn't interfere with all your top-rail accessories.

Folding iron sights like the Magpul MBUIS have become a popular choice because they offer performance and accuracy like a fixed rear  A2-style sight, but they can be quickly folded down to offer an unobstructed view through your red dot or optic. And if your optic ever goes down, the folding sight simply pops back up with the push of a spring-loaded button.

Fixed Front, Folding Rear

Why not use the best of both worlds? We’ve stopped trying to justify one over the other and said to Hell with it. We like to use a fixed A2 front sight with a rear folding sight, pictured above. This combo affords a rugged, strong front sight post that can take abuse like a champ. At the same time, one can fold the rear sight out of the way and enjoy a clear sight picture through any optic. And by installing a set of scope rings at least 1" high, you can throw any magnified optic on your rifle without any clearance issues.

Co-Witnessing Your Optic and Irons

If you’ve browsed any tactical rifle or optic forums, you’ve probably come across the phrase "co-witness". Most shooters are curious if “X optic” will co-witness with “Y irons”. To break it down very simply, co-witnessing is how your optic and iron sights provide individual sight pictures without interfering with one another. This buzzword is what lets you rock both irons and an optic without having to remove either.

Absolute vs. 1/3rd Co-Witness

More buzzwords! Absolute and 1/3rd co-witness simply describes how your iron sights and optic work together to provide a clear sight picture and comfortable shooting position.

Absolute co-witness means your front and rear iron sights perfectly line up with your optic's red dot or point of aim when you get your sight picture. An absolute co-witness allows you to quickly verify that your rifle is zeroed. If the point of aim on your irons and optic don't line up, you know you need to make some adjustments. If, for some strange reason, both your rear iron sight and optic were to fail, you could use your optic's tube or housing as a rough "ghost ring" rear sight in tandem with your front sight post to put rounds down range in an emergency.


  • Perfect for low cheek rest
  • Sight sits lower on rifle
  • Increased accuracy
  • Reduced profile
  • Immediately verify zero


  • Obstructs sight picture
  • Low cheek rest interferes with hearing protection
  • Large optics may interfere with rear iron sight

One-third co-witness describes shifting your optic's point of aim so that it is above and out of the way of your front and rear iron sights' combined point of aim. This provides a clearer sight picture and it makes shooting in low-light conditions much easier.


  • Clearer sight picture without obstruction
  • High cheek rest reduces neck strain
  • Easier to pull sight picture with ear pro
  • Large optics clear rear iron sight more easily

Benefits of Co-Witnessing

Regardless of which method you choose, the primary benefit of co-witnessing your sights is having a reliable, no-lens, no-battery option of aiming if your optic breaks. Optics these days can be extremely tough and many are made to go to war. But at the same time, they utilize glass and electronics. This complicates them and presents a multitude of potential failure points. Iron sights are simple and fail-proof, short of being crushed or hit hard enough to break. The U.S military uses CompM4 red dots - one of the most rugged red dots you’ll find - but they still equip all their rifles with good ole’ A2 front posts and a rear BUIS.

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