TFB Review: Primary Arms SLx 3x MicroPrism

Daniel Y
by Daniel Y

Primary Arms has been steadily improving and expanding its range of optics. The lineup of prism scopes has grown and undergone revisions, and the MicroPrism family is the current flagship. This review will cover the SLx 3x model, which sits between the 1x and 5x versions.

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Disclosures are critical in any review. Primary Arms provided the optic for review. I bought the ammo and used it on a range of my guns. I do not have a prior relationship with Primary Arms. This is my first review of a PA product.


Prism sights are not new. The US used a prismatic Warner & Swasey scope on 1903 Springfield sniper rifles in World War 1. But in the modern era, the ACOG is probably the best-known example, in no small part thanks to its adoption by the US military.

Most of my personal experience with prism optics is from the ACOG series. I have used the TA11 3.5x on my go-to AR-15 for many years. In my time at the gun store and shooting range, I have tried several other versions, and I owned a Vortex 1x prism for a time.

The current MicroPrism series is not the first prism scope family from Primary Arms. They sell, and have sold, various models in 1x, 2x, 3x, and 5x power ranges. But the MicroPrism series is the current flagship series, emphasizing sleek design and small footprints.

Primary Arms includes ballistic information for a range of popular calibers and how those correspond to the drop marks in the reticle.

Mounting System

One of the most interesting parts of the SLx MicroPrism is the mounting system, which is very flexible. It includes three cantilever sections and a riser. Mixing and matching those pieces can place the optic right where it needs to be to get proper eye relief. That matters a lot for a prism optic because the eye relief tends to be much shorter than traditional scopes.

Three fasteners clamping the optic to the rail have T-25 Torx heads. All of the fasteners on the underside of the optic have 2.5mm Allen heads. Primary Arms includes an array of screws of various lengths to work with the range of spacers.

The attached spacer out of the box works on most guns, including this SIG SG551.


As you would expect on a Primary Arms optic, the SLx 3x MicroPrism has an ACSS reticle. There are two main parts of the reticle. The inner reticle has an illuminated chevron and Christmas tree-style reticle with drop and wind hold marks. An outer ring surrounds the inner reticle and is the appropriate aiming point for running targets.

The illumination is pretty good, but not incredible. It contrasts nicely against a black background but is not “red dot bright.” I mostly used the SLx 3x with the illumination turned off but did use it at times when I wanted more contrast, like in an indoor range.

On The Range

Zeroing the SLx 3x MicroPrism was uneventful each time I switched guns. The elevation and windage turrets have 1/4 MOA adjustments. The turrets are an exposed, flush-style that requires a flathead screwdriver to adjust. When I did not have a screwdriver handy a small key also worked. It is always good when there is not a lot to say about zeroing. The MicroPrism tracked well with each adjustment and it did not lose zero through shooting or handling, or bumping around in the floorboard of my vehicle.

How It Looks On Different Guns

I used the SLx 3x MicroPrism on an array of firearms. This optic can work on most guns, and here are some pictures on a range of different guns:

Anderson Manufacturing AR-15 Dissipator



Rock River AR-15 with A2 Upper

Brownells 733 with C7 (A1) Upper

The standard configurations worked on the first three guns. I switched the mounts around to try and optimize it, but the standard layout worked best. That arrangement provided enough clearance to avoid most rear sights.

Carry Handle Usage

Use on a carry handle requires the purchase of an additional screw from Primary Arms. It fits the threads of the MicroPrism mounts and includes a curved spacer that fits against the rounded underside of a carry handle. I used the longer extended mount to move the optic as close to my eye as possible. This configuration worked on my A2 uppers.

However, it didn’t fit on my A1 uppers. In the rearmost setting, the scope base interfered with the rear sight aperture. I found that moving the scope base forward by one screw position it worked fine. This was less optimal with the eye relief, but I compensated by running the stock one position shorter.

For A1 uppers, the mounting screw needs to go into the second threaded hole, not the first like on the A2 uppers.

The extended spacer has a hidden bonus feature. There is a hole running the length of the spacer that lines up with the iron sights. The view is not as good as the totally unobstructed sights, but it is usable. It was a nice touch by Primary Arms to include this.

While the focus is not great, the visible area through the mount is visible here.


For $320 (or even less on sale), the SLx 3x MicroPrism is a heck of an option. Without adding much weight or bulk it dramatically improves target hit probability at distance compared to similarly-sized 1x sights. It is not, however, a heavy-hitter for real long-range work. This would be totally wrong on a heavy bolt gun. But on most common semiautomatic platforms it is a great way to pick up ranged capability without making the gun bulky or chunky.

Check Prices on Primary Arms SLx 3x MicroPrism Scopes

I particularly like the SLx 3x MicroPrism on a carry handle build. It is a cost-effective way to add useful magnification without obstructing the sights. Whether you are a newcomer to carry handle builds, or if you have an old Colt Sporter in the back of your safe gathering dust, adding one of these optics is worth considering. No, it’s not “clone correct,” but it looks good and performs great.

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Daniel Y
Daniel Y

AKA @fromtheguncounter on Instagram. Gun nerd, reloader, attorney, and mediocre hunter. Daniel can still be found on occasion behind the counter at a local gun store. When he is not shooting, he enjoys hiking, camping, and rappelling around Utah.

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2 of 5 comments
  • Brodie Brodie on Mar 11, 2024

    Would you pick this or the TA11 for a carry handle build? Looking at the spec sheets seems like the prism is the better choice with more forgiving eye relief and better field of view at half the weight.

  • TomP TomP on Mar 14, 2024

    I own two of these (red & green, both 300 BLK) and they are great. While some magnified optics beg for an auxiliary RDS for very short ranges (like 10'), this 3x optic is fine without. The ONLY negative I've found is that the diopter adjustment is way way too fine . . . there are about TWENTY turns on the diopter so it's a bit of a PIA to find the optimal adjustment. Two or 3 turns of adjustment would be plenty enough. Apparently I'm not the only one to notice this because PA made a video specifically about microprism diopter adjustment if you can imagine that.