The Primary Arms SLx MD-25 ACSS Red Dot


The Primary Arms SLx MD-25 ACSS Red Dot

The Primary Arms SLx MD-25 ACSS Red Dot looks great and runs just as well. IMG Rob R.U.S.A. -( The old adage of “You get what you p

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The Primary Arms SLx MD-25 ACSS Red Dot looks great and runs just as well. IMG Rob R.

U.S.A. -( The old adage of “You get what you pay for” when it comes to optics is becoming less and less true every year – especially with optics like the Primary Arms SLx MD-25.  We have entered somewhat of a renaissance of electro-optics, which began, roughly in the early 2000s with the wide adoption of optics like the Aimpoint M68 and EoTech by the US military.  The civilian market quickly caught on, especially as the unholy 90s “assault weapon” ban came to an end in 2004, and ARs and other modern rifles came back in a big way.  Now, ‘iron sights’ and ‘back up iron sights’ on an AR are almost synonymous, as almost every AR or AK you’ll find on the range or at a training class is sporting some kind of optic as its primary sighting system.

There once were generally two choices:  A high dollar ($400+) option from suppliers like EoTech, Aimpoint, Trijicon, and Leupold; and a budget option ($150 and under).  The budget options were, generally speaking, of somewhat poor quality and overall lacking in reliability, durability, fit and finish, and features.  Companies like Holosun and Primary Arms have very much bucked that trend in recent years, however offering quality, durability, reliability, and features that can hold their own against many higher-end optics, at a fraction of the price.

Primary Arms SLx MD-25

One such optic is a new red dot from Primary Arms, called the SLx MD-25, which retails for $170 for the 2 MOA dot model.  If you’re short on time, the best way I can describe the MD-25 is that it’s a budget competitor to the Trijicon MRO, with a much more versatile reticle.  The MD-25 is what I would call a ‘mid-sized’ tubular red dot.  It’s dimensionally larger than a micro dot like the 20mm Aimpoint T1 or Holosun 503, but still smaller and lighter than the Aimpoint 30mm models like the CompM4/M68.

Lightweight, clear and durable, the Primary Arms SLx MD-25 is a solid choice. IMG Rob R.

The MD-25, like the Trijicon MRO, features a 25mm window, thus giving you an optic with a near micro-like weight and size, but increasing the window size half way to that of a full size 30mm optic.  Going from a 20mm micro dot: what effect does the extra 5mm in glass and viewing area actually have?  When I shot three rifles I had with different sized optics mounted on them – one with a 20mm Holosun 503, one with the 25mm MD-25, and one with a 30mm Aimpoint PRO – I found that my ability to quickly find the dot from awkward shooting positions where my head wouldn’t be perfectly lined up behind the glass was considerably improved going from the 20mm to 25mm optic, but not noticeably better going from the 25mm to 30mm window size.  25 millimeters seems to be a kind of sweet spot of lens sizes for tubular red dots, at least for myself.

If you decide you like the idea of a 25mm red dot and want to know what you can expect to get for that $170 dollars – here are a few for the MD-25:

PA SLx MD-25 ACSS Fit and Finish

The fit and finish of the MD-25 is without question on par with optics I’ve found that are three times or more its price, such as the MRO.  The actual finish on it is a very nice scratch and abrasion resistant matte black – no complaints there.  The overall feel and look of the aluminum housing is also quite impressive for the price, and seems very similar to the Primary Arms 1x Cyclops, which I personally took scuba diving down to 130 feet with no failure to the optic.  Granted, that was prism optic, and I wouldn’t expect the MD-25 to withstand that same kind of abuse, but the build quality seems very on par with other optics from Primary Arms with a reputation for durability that I have experience with.

The Primary Arms SLX is compatible with NVGs for use in low, or no-light conditions. IMG Rob R.

Night Vision Compatibility   

The MD-25 has two different night vision settings, which is impressive given that the night vision feature alone on many optics can cost you almost as much as the total cost of the MD-25.  How well and how bright the night vision settings work on the MD-25 is not known to me, as this wasn’t something I was able to test.  My one concern though is that even on the lowest of the night vision settings the reticle might end up being a bit on the bright sight under NVGs.  My reason for saying this is that, in pitch black with eyes adjusted to the dark, I can faintly make out the reticle on the dimmest NVG setting.  On other optics I have this feature on, such as my EoTech EXPS3, the reticle is completely invisible to the naked eye.

Mounts Compatibility:

Unlike the MRO, the MD-25 uses the widely available Aimpoint T1 footprint, which you can find many many types and brands of in the aftermarket.  The mount I used for testing was the Unity Tactical FAST mount (stay tuned for that review), and the MD-25 dropped in secure without issue.  The optic also comes with several different height mounts, included, all of which have a similar and impressive quality to them for what you pay.

Something to note, however, if you’re using an aftermarket mount made for a 20mm red dot like the T1, is that since the MD-25 has a 25mm piece of glass, it will sit slightly higher than a 20mm optic would on the mount.  Thus, a flip to side magnifier (or flip to center magnifier mount, like the Unity Tactical version I tested) will not perfectly line up behind the MD-25, and will sit slightly lower than the red dot.  I did not find this to be much of an issue when actually using the magnifier, however.

The SLx MD-25 pairs well with a magnifier for extended range. IMG Rob R.


There is currently a standard 2 MOA dot version of the MD-25, for the red dot purists.  However, Primary Arms will soon be releasing an ACSS reticle version that features a chevron with three BDC dots beneath it, centered in a 65 MOA horseshoe reticle.  This is the version I was able to test out, and it’s quite helpful in making those longer shots, as well as increasing my dot acquisition speed up close.  The math that goes into the reticle allows the shooter to also use the BDC for a multitude of calibers; use the chevron and BDC dots as a range estimator, and use the open ends of the chevron to lead moving targets.

Some things to note on the BDC dots however are that, unless you have eagle vision, to really see and be able to effectively use the BDC dots you need to run a magnifier behind the MD-25 ACSS.  Without magnification, the dots appear (to my eyes) to be too close and clustered together to discern the individual dots.  That said, without magnification, the effect of a small chevron stacked on top of three small clustered dots produces a sort of illuminated front sight post of sorts, which having first learned to shoot on the M16a2 was a familiar thing that I quickly took to. Lastly, I found the reticle to be quite crisp compared to older models from both Holosun and Primary Arms, so the technology seems to be progressively improving.

Primary Arms SLx MD-25 reticle showing the chevron, outer donut, and subtentions. IMG Rob R.


The MD-25 uses a standard CR2032 battery and has an estimated 50,000-hour battery life for the 2 MOA model.  The battery life depends on several factors, such as the make of the battery and the brightness setting you leave it on.  Also, the ACSS reticle version will undoubtedly have a shorter battery life than the 2 MOA dot version, but almost any way you cut it, you’re looking at a battery life of several years on a single battery.  Throughout my testing, I did not observe any flickering of the reticle under recoil or any hiccups when spinning through the brightness settings – a common problem I’ve observed on lower-quality optics. The windage/elevation and battery compartment turrets, and battery terminal, are all very robust and secured, and I’m confident the build quality of all these components will prevent the electronics of the unit from suffering a total failure under heavy abuse.

Whether you decide to go with a 20mm micro red dot, 25mm ‘mid-size’, or larger 30mm M68-size optic, you can rest assured that these days there are plenty of makes and models of each that will serve you well without having to break the bank.  The Primary Arms SLx MD-25 is one of those I’d recommend if you’re in the market and looking for a cost-friendly, smaller/lighter red dot with a larger 25mm window.

About Rob R.

Rob R. is a US Army / Iraq War veteran with a love for liberty, firearms, BMWs, and cats. After his military service, he worked for 9 years in 14 different countries across the African continent as a military advisor and trainer – preparing African Union peacekeeping forces for deployment to various conflicts in the region, under the US State Department’s ACOTA program. A Florida native, he currently resides in southwestern PA.

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