Magpul MBUS 3 Rear Sight

The Magpul MBUS rear sight, third generation, folds to just 0.55 inches high and weighs a scant 30 grams with hardware, making it one of the least intrusive backup sights you can put on a rifle. It brings together the best features, strengths, and value of the original MBUS and the MBUS Pro in a feature packed back up sight system. Crucially, it adds a windage adjustable, rapid select aperture that earlier folding sights could not match.

What the Magpul MBUS Rear Sight Adds to a Build

Rear sights carry more responsibility than front sights on an AR. The rear aperture is where windage is adjusted, and it is the element that determines how quickly you can pick up a sight picture under pressure.

The MBUS 3 rear answers both with a windage adjustable, rapid select aperture system. Rapid select means you can switch between apertures quickly, which is the difference between a precise small aperture for deliberate shots and a large aperture for speed at close range.

It belongs on any AR that carries an optic, because a backup that stays folded and weighs an ounce is essentially free insurance against a dead battery or broken glass. It is equally at home on a rifle running no optic at all, where the folding aperture becomes the primary sighting system.

Key Features

• Windage adjustable rear aperture so you can zero the irons independently of your optic
• Rapid select aperture system for switching between precision and speed
• 0.55 inches high folded and 1.38 inches at its widest point
• Weighs just 30 grams including hardware
• Impact resistant polymer construction that is lightweight and extremely durable
• Spring loaded deployment through an ambidextrous push button

Magpul MBUS Rear Sight Height, Weight, and Aperture System

Half an inch of folded height is what makes this sight usable under a red dot. If a backup sight sits too tall when folded, it clutters the bottom of your optic window and you end up removing it, which defeats the purpose entirely.

Thirty grams is genuinely negligible on a rifle that weighs several pounds. Combined with impact resistant polymer construction, that low weight is achieved without the fragility people used to associate with plastic sights, because polymer absorbs impacts that would permanently bend a thin steel aperture. Its aesthetics come from the MBUS Pro, and MBUS 3 sights are offered in Black and Flat Dark Earth. See the full family at Magpul.

Practical Use, Care, and Zeroing

Mount the sight as far to the rear of your receiver rail as the optic allows. Sight radius is the distance between front and rear sights, and a longer radius reduces the effect of small aiming errors, so every inch you gain at the back is worth having.

Zero the irons for real. A Magpul MBUS rear sight that has never been zeroed is decoration, and the whole value proposition depends on it being ready when the optic quits. Fold the optic out of the way or remove it, zero at 50 yards for a practical AR setup, then fold the sights down and forget about them.

Deploy and fold the sight periodically so the spring and detent stay free, and keep grit out of the hinge and the windage mechanism. Wipe it down when the rifle gets cleaned and confirm the crossbolt is still snug a few times a year. Pair it with a front sight, optic, and mounts from our optics category.

The Simple Argument

Electronics fail at inconvenient times, and glass breaks. A folding rear sight that adds an ounce, disappears when folded, and gives you a windage adjustable aperture when deployed removes an entire failure mode from your rifle for very little money.

Install it, zero it, and forget it until you need it. Ships direct to your door, no FFL required.