Magpul MBUS Rear Sight Review
December 15, 2013

Magpul MBUS Rear Sight Review

Over the past couple of years, I have started to form some strong opinions on what I like on my AR style rifles.  One of my latest revelations has been that every AR needs to have some type of Back Up Iron Sights (BUIS).  Knowing that I have a back up sight system that doesn't need batteries or knowing that I have a sight system that is not sensitive to an EMP or solar flares seems to make sense. I wouldn't consider myself a doom-n-gloom-er, but I do sleep better when I feel I have my gear in order and redundancy in a sighting system just seems to be a critical part of getting my gear in order.

There are some things that need to be considered if you are planning to have back up sights, such as your primary optics style and length, mount style and height, co-witness or not, the need for quick detach features and ensuring your back ups are zeroed.  Then there is another set of things to consider when deciding on a set of BUIS, such as aluminum, steel or polymer, fold down or fixed, mount locations and your budget.  There are probably more, but I think you get the picture.  I don't go into all these decision points in this review, but keep in mind that a rifle configuration with back up sights is a system of parts that must be somewhat integrated to have an optimum configuration.

Today there are a wide variety of BUIS on the market and over the past couple of years Magpul has added their versions to the mix.  Magpul recently released a new version of BUIS (MBUS® Pro) that are all steel and Magpul intends to compete with other metallic sight manufacturers.  For this review, I decided to go with their polymer sight, the Magpul MBUS Rear Sight, to use on a recent AR build where I needed a fold down rear sight and the Magpul polymer sight had an attractive price point.  Magpul's MSRP on their rear sight is $57.95, which is pretty competitive for a rear back up sight.  Sure, there should be a difference in cost for a polymer sight versus a metallic sight and this difference is clearly reflected in the price on the MBUS Rear Sight.  I actually purchased the rear sight at my local gun store for $52.99, which seems to be a relatively common retail price.  Since my AR had an integrated fold down front sight as part of the gas block, I only needed a rear sight to have a complete set of BUIS.  I'm hoping that this close look at the rear sight will give me a good idea on what to expect from a Magpul MBUS Front Sight.


The following information in colored italics was taken from the Magpul website on 12/5/13 and gives their description, key features and specifications for the Magpul MBUS Rear Sight.


  • The MBUS (Magpul Back-Up Sight) is a low-cost, color injection molded, folding back-up sight.
  • The dual aperture MBUS Rear Sight is adjustable for windage and fits most 1913 Picatinny rail equipped weapons, but is specifically tailored to the AR15/M16 platform.
  • Made in U.S.A.


  • Impact resistant polymer construction provides light weight and resists operational abuse
  • Spring-loaded flip up sight easily activated from either side or by pressing the top
  • Detent and spring pressure keeps sight erect but allows for unobstructed folding under impact, etc.
  • Clamps to MIL-STD-1913 Picatinny/STANAG 4694 receiver rail and provides the same height-over-bore as standard A2 irons
  • Protective wings shield the dual, same plane flip apertures
  • Sight can still be folded with either large or small aperture in position
  • Detent knob easily and positively adjusts windage


  • MBUS – Rear Gen 2
  • Weight, w/ hardware: 1.3 oz.
  • Height above rail, stowed: ~0.51 in.
  • Center of aperture to top of rail: 1.42 in.
  • Length, stowed: 2.6 in.
  • Length, deployed: 1.5 in.

The sight came packaged as shown below.

Figure 1                                                                Figure 2
Magpul MBUS Rear Sight Review  Magpul MBUS Rear Sight Review

Inside the package was only the rear sight assembly.  I will be honest that I did have some concerns that this tiny complex polymer assembly may give me the impression of cheap plastic when I took it out of the package, but I had faith in Magpul and my impression was very positive.  My first impression was more along the lines of "impressive."  The sight was tight with no looseness and popped firmly into place when pressing the release.  The sight is nearly all polymer (most likely glass filled nylon) except for the spring, pins and screws.

The sight shown in this review is a generation 2 (Gen 2) sight.  Magpul released a PDF file explaining the differences between the Gen 1 and Gen 2 sights and you can view the file at this link.  Basically Magpul states the Gen 2 sight "features a slimmer profile for increased optics compatibility and a positive detent to securely lock the front sight post in place."   The graphic below shows a comparison in size of the Gen 1 versus Gen 2.

Figure 3
Magpul MBUS Gen1 versus Gen 2 Sight Profile

The sight measures 2.60" in length and 1.50" in width.  When the sight is deployed (up), it measures about 1.46" in length.

Figure 4
Magpul MBUS Rear Sight Review

The photo below shows how the sight is locked into place in the stowed (down) position.  You can also see that pushing the release lever down disengages the lever from the notch in the sight.  The spring loaded action then pops the sight up.

Figure 5
Magpul MBUS Rear Sight Review

The site body and peep portion have index marks for reference so you can go back to your windage zero in the event you remove the sight and use it on another rifle.

Figure 6
Magpul MBUS Rear Sight Review

The clamp bolt appeared to have some blue thread locking compound on the screw.

Figure 7
Magpul MBUS Rear Sight Review

The rear sight assembly weighed in at 1.3 ounces just as stated in the specification.

Figure 8
Magpul MBUS Rear Sight Review

These next photos show the sight installed on an AR style rifle with the sight in the rear most position on the upper receiver rail.  When the sight is in the deployed (up) position, the center of the peep hole measures about 1.43" above the top of the rail and this provides the same height as A2 style iron sights.

Figure 9                                                             Figure 10
Magpul MBUS Rear Sight Review   Magpul MBUS Rear Sight Review

The sight installs on the rail by removing the single clamp bolt, removing the charging handle on your AR and then sliding the sight forward from the rear of rail.  Once you line up the clamp bolt hole with the slot in the rail, you can then install and tighten the clamp bolt.  The instructions below were inside the cardboard packaging.

Figure 11
Magpul MBUS Rear Sight Review

When you press the front area of the sight or the two side tabs, the rear portions is spring loaded and pops up into the deployed (up) position.  The sight can be lowered and put in the stowed (down) position just by pressing on the upper portion of the sight and rotating it to the down position.  You do not have to press the release to stow the sight.  The windage adjustment knob is marked with an arrow to indicate the direction to turn the knob to shift the bullet impact in that direction.  There are detents at every 1/10 turn of the knob.  The knob has firm resistance and securely seats in the detents and I feel it would be difficult to accidentally rotate the knob.

Figure 12
Magpul MBUS Rear Sight Review

The sight comes with two different diameter aperture holes for the peep configuration.  With the front peep rotated up, the hole is about 0.10" in diameter and with the front peep rotated down the rear peep is about 0.20" in diameter.  The front smaller diameter peep had firm resistance rotating it between positions (up or down) and also had detents which held it in either the up or down position.  The way the front peep is designed, it has the "same plane" position on the sight.  I'm not sure if this is any real advantage, but it is something that Magpul believes is worth pointing out.  The peeps are protected by two wings that shield the peeps on each side.

One thing to note is that when the sight is folded to a stowed position, the front smaller diameter peep must be positioned against the rear larger peep so that the stowed position of the sight has a minimum height.  If you have minimal clearance between this sight and your optics (like shown further in this review), you will need to stow the sight at a minimum height.

Figure 13                                                              Figure 14
Magpul MBUS Rear Sight Review  Magpul MBUS Rear Sight Review

Another sight configuration for the Magpul MBUS Rear Sight is the NAWS (No Aperture Window Sight) configuration.  Both peep sights fold forward so that you are looking over them at your front sight.  This allows for maximum visibility with your dominant eye.

Figure 15
Magpul MBUS Rear Sight Review

In this next photo, my sights were already zeroed and I tried to put the front post at a height that would match looking through the sight in the NAWS configuration.

Figure 16
Magpul MBUS Rear Sight Review

I installed the Magpul MBUS Rear Sight on one of my recent AR builds as shown below.  For this build, I purchased a fully assembled RGuns upper assembly and a stripped RGuns lower assembly which I finished out myself.  I then installed the Magpul MBUS Rear Sight and a Bushnell AR Optics AR/223 1-4x24 Throw Down PCL Riflescope with a set of Warne Maxima Quick Detach Rings.

Figure 17
Magpul MBUS Rear Sight Review

You can see that with this setup there is very little clearance between the Magpul sight and the power adjustment ring, but there is enough clearance for the scope to function properly.

Figure 18
Magpul MBUS Rear Sight Review

The Magpul sight zeroed without issue and I was pleased with my range session using the back up sights only.


Bottom Line:

I think back up iron sights (BUIS) are a must for every AR and the Magpul MBUS sights seem to deliver a good quality, functionality and value for those on a budget.  The MBUS sights will save you both weight and money.  There is no doubt that strength and durability of steel sights cannot be matched with polymer sights and you need to consider if the added strength and durability outweighs the value and functionality of polymer sights for your rifle's intended role.  For me and for this rifle, I'm completely satisfied that the Magpul MBUS Rear Sight is the right rear sight for this rifle.  It is well protected tucked away under the ocular housing and hopefully I never will need to use my backups.  If I do, then I feel certain it will be zeroed and ready should that time come.  I can clearly see myself purchasing more of the Magpul MBUS sights in the future and in fact,  I just ordered a front and rear set for another rifle.

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