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Review - A.R.M.S.® #40 Flip up Sight

Updated: Aug 4, 2022

History of A.R.M.S.

A.R.M.S. (Atlantic Research Marketing Systems) was founded in 1980. The business goal was to create, manufacture, and market advanced products for the shooting public. Products developed and manufactured are in use by US Armed Forces as well as within several global military forces.

For more information about A.R.M.S. and to check out their products, click here A.R.M.S. website.

Why A.R.M.S.?

With the influence of SEAL Team and searching amongst the promotional images for kit and equipment, I came across this still from an episode. Looking specifically at Clay and Jasons rifle I saw the rear flip up sights and wasn't exactly sure what they were, but knew I wanted to know more...

After a lot of googling and comparisons I found that they were either the A.R.M.S. #40 Flip up sights or the A.R.M.S. #40 A2 Flip up sights. This was based upon the large circular windage adjustment wheel on the left hand side, the separate rail attachment block (at the front of the sight) and the curved front top of the sight which is somewhat unique in looks. Both the #40 and #40 A2 are near identical apart from the sight reticle. The #40 pictured on the left below, has 1 circular aperture, whilst the #40 A2 pictured on the right below, has 2, a larger and a smaller. From the SEAL Team image above I believe that the variant used is the original #40.

I want to take this opportunity to say thank you to A.R.M.S. for their kind permission to use their product photos in this review. By doing so, this enables you to see the product in high quality imaging. Thanks guys!

Product details

Herein lies the product description from the A.R.M.S. website;

  • A.R.M.S.® #40™ Stand Alone Flip-Up Sight

  • Spring loaded and repeat zero

  • Rear quick release lever

  • Horizon line notch

  • 500 - 600 meter sight

  • Windage adjustments

  • .75 MOA.

  • Weight .1875 lbs (85.04g)

  • Dimensions 3 × 2 × 2 in (55 L x 35 W x 30 H mm)

  • 100% made in the USA

  • Pat. No. 5533292


What does it actually mean?

So to cut through a couple of the lesser known details above I've pulled out the parts that may be of interest;

  • Horizon line notch - the 'HLN' is primarily designed to be used for snap shooting, but also serves the purpose to be minimalist so that an ACOG can sit back over the top of the sight without obstruction.

  • .75 MOA - a 'MOA', or Minute of Angle, refers to the capability that a firearm has to consistently deliver a grouping of shots at a particular distance. For example: One MOA = at 100 yards (91.44m) is a 1” group.

  • Pat. No. 5533292 - a patent number assigned by the United States Patent and Trademark Office. A patent for an invention, is the grant of a property right to the inventor. The below image is a copy of this patent.


A.R.M.S. #40 in detail

Front & Left hand side view


The sight is low profile and whilst standing at 30mm when collapsed, it's marginally taller than a MBUS (Magpul Back Up Sight). As can be seen in the left hand image, on the bottom left is the rail attachment block (RAB) held in place by a 3mm thick screw (see below section for right hand side view). The rail bite width is 21mm. Handily the RAB has an arrow marking the way it should be facing. Behind the block to the right is the 'swan' logo. Above at the rear is the windage (.75) adjustment wheel. On top of the sight at the front in the centre is the tension spring that enables the flip up motion. Of note is that this is in my opinion a slight issue. Potentially if used within a sandy or humid environment due to sand and water ingress, the spring will likely be requiring more regular cleaning.


When the sight is flipped up, it stands at 47mm tall. As shown in the image on the right, two sights can be seen. In this image the 'Horizon Line Notch' (HLN) is not being used. The HLN is designed to be used when the rifle is being fired without the main sight flipped up, such as in a ambush or potentially if the optic has been damaged and removed. This is generally a backup backup sight. The left and right of the HLN are identified by the white V shaped markings for the user to focus their vision through. In this second image, the 500 - 600m sight is active and is adjusted left or right by turning the windage adjustment wheel on the side.

Right hand side view


On the right hand side of the sight and starting at the rear, the angled metal rod / lever pointing to approx 1 o'clock (Image A) is in fact the quick release lever. By pressing downwards on top of the rear of the sight, the lever can be pulled back allowing the sight to flip up. The lever then under tension snaps forward laying flat (Image B). When laid flat, it fits underneath the main sight section. This is designed so if the weapon is dropped and the sight folds, it doesn't damage or alter the sight or lever. This lever and fixing combination requires the sight to have a small cutout section as seen when the sight is upright (Image C). In front of the lever is the windage adjustment screw. The top section further bears the A.R.M.S. logo. At the front of the sight is the RAB screw which is attached directly to the sight via a metal corded ensuring that if you unscrew it too far and the screw comes out, you won't lose it.


When the sight is upright, the only additions to the above notes are that the quick release lever cutout can be seen more clearly and the rear of the sight has the Swan logo stamped on it.

The below two pictures illustrate the RAB having been removed, exposing the 3mm pin. As mentioned the screw end is attached to the sight as it is definetley a small part. The design of the pin as can be seen is not a standard circular type. By creating a square pin this ensures that when fitting between the rail teeth there are no gaps or potential for the sight to wobble, another neat feature to make this sight solid when fitted.

Sight fitted to rifle

Fitted to an HK416 and with a EOTech EXPS2 style sight also fitted, it can be seen that the sight is low profile and doesn't obstruct the holosight picture. The 2nd image shows the sights' height when compared with the EXPS2. The reticle clears the bottom of the EXPS2 window allowing the user to still aim.

Rear views fitted to rifle

Top left - provides a basic idea of obstruction / vision of the sight and the EXPS2.

Top right - sight stowed and HLN active.

Bottom left - sight upright and HLN active which lines up with the lower part of the EXPS2.

Bottom right - sight upright and standard aperature active similar to the HLN.


Thoughts and opinion

The #40 sight is no doubt a rugged and well used piece of kit. It's almost certainly appealing to some and exerts hisses of panic from others, it comes down to personal preference. Compared to the famous MBUS Sight Rear designed by Magpul there are several differences. Firstly is the price. The #40 is not cheap and it's not polymer. It's genuine milspec metal and is built to last. It's unique design and look on a variety of rifles will certainly set it apart from the other polymer flip ups. My only negative would be the spring on top being open to the elements therefore requiring cleaning after a days use. Having fired over 200 .22 rounds with the sight mounted, there was no discernible movement of the whole sight structure or any movement from the HLN or 500 - 600m sight. With .22s obviously the recoil of the rifle is slight, so there is no movement of the sight, however with the ability to really tighten down the sight onto the rail, I doubt that this will go anywhere quickly on a 5.56 rifle. The whole sight looks good, feels good and on the right rifle completes the picture. The #40 is now attached to the HK416 and is another piece to the puzzle to completing the SEAL Team accurate rifle.


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Final Note

I am not paid for my blogs by the manufacturers or companies that I purchase my items from. I am not offered freebies to promote a product. These blogs are purely written from my own experience in truth to help advise and inform others who may wish to purchase the items or understand more about them. If I am sent a freebie to review this will be stated at the beginning to make you aware.

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