Primary Arms Classic Series 21mm Micro Reflex Sight (Image courtesy JWT for
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The number one review request I get is “budget optic reviews.” You’ll see the Primary Arms brand in a fairly high percentage of those reviews, as they consistently deliver quality above their price point.

The Primary Arms Classic Series 21mm Micro Reflex Sight is no different. For a very low price of entry, Primary Arms has delivered a reliable red dot pistol optic in a narrow format, perfect for use with popular firearms like the P365 and G43X MOS.

According to people without an irregular astigmatism (that’s not me), the 3MOA dot reticle is crisp and round. This is born out in photos as well.

Image courtesy JWT for

The 21mm form factor is fairly narrow, but still large enough to get a solid sight picture.  The choice to make this a rectangular screen with a fairly narrow 6061-T6 aluminum housing means that every millimeter of potential screen space is available for use.

That screen space is clear, but with some bluing and slight dimming of the image in low light.

There are 10 brightness settings, but none specific to NV optics.

The Classic Series 21mm Micro Reflex Sight has no “shake awake” or instant on feature, nor is there any automatic brightness adjustment. On the medium setting, a single CR2023 battery (one supplied) should last well over 30,000 hours. That’s almost three and a half years.

I never turned this one off and it’s lasted 3 months and counting. As the battery is mounted on the bottom, you’ll have to unmount, remount, and then re-zero the optic each time you swap out the battery.

Image courtesy JWT for

You’ll need a very small hex key (one is supplied) to adjust the windage and elevation. Those adjustments should be 1 MOA “per click,” but there are no clicks. I couldn’t hear or feel any response from the adjustment screws. The adjustment itself is very smooth, so as you look through the optic, it’s pretty easy to simply turn the screws and watch the dot move to where you want it.

Image courtesy JWT for

Despite its low cost, I have no concerns with the Primary Arms 21mm MRS when it comes to reliability. I’ve now put several thousand rounds under this optic through a variety of pistols and a Remington VersaMax shotgun on a Picatinny mount. The dot never moved unless I wanted it to and never failed in any way.

Controls are simple enough; “+” for on and brighter, “-” for dimmer. Hold both buttons down to turn it off. Bare-handed I had no problems getting the controls right, but they were too small to use with any kind of gloves on.

Image courtesy JWT for

Primary Arms doesn’t list any waterproof rating for the 21mm MRS and there’s none mentioned in the manual. Since it’s an open bottom design, with the battery exposed, water resistance is likely to be minimal. I went ahead and swiped it through the shower spray a few times it while mounted on a pistol there was no ill effect.

What’s nice is that this lower-priced optic is still covered by the Primary Arms Lifetime Guarantee. Primary Arms is well-known for their quality customer service, and their Lifetime Guarantee is great.

The Classic Series 21mm MRS wouldn’t be my choice for a duty optic, but it’s a solid choice for folks on a budget who want or need a reliable red dot sight for their pistol. That’s especially the case for semi-autos with narrow slides, common with today’s popular EDC guns.

SPECIFICATIONS: Primary Arms Classic Series 21mm Micro Reflex Sight 

Battery Life: 25,001 – 50,000 Hours
Battery Type:  CR2032 3V Lithium Coin
Brightness: 10 Settings
Click Value: 1 MOA
Material: Aluminum – 6061-T6Country of Origin: Made in China
Optic Series: Classic
Reticle: 3 MOA Dot
Reticle Color: Red
Warranty: Lifetime
Weight.: 5.6 oz
Height: .86″Length: 1.58″
Total windage adjustment: 60MOA
Total elevation adjustment: 60MOA
Price: $149.99

Ratings (out of five stars):

Overall * * *
Zero frills. There’s no “shake awake” or auto on, but the battery will last for years…literally. The dot is crisp and clear, but there’s a little bluing present through the glass. The lack of “clicks” is annoying, but the Primary Arms 21mm Sight certainly handles recoil and never skipped beat. For under $150, the Primary Arms Classic Series 21mm Micro Reflex Sight is a very solid, affordable choice.

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  1. Last year I purchased 3 sale priced stripped AP AR-308 lower receivers and two AP stripped upper receivers from PA, components arrived in pristine condition. Purchased the last AP stripped upper from another bargain priced free ship seller because AP 308 fit and finish is no worry consistent.
    Buying from PA was quick and easy and they do answer the phone, etc.

    • Yea it’s well known that PA offers a very competitive price for quality goods. No reason to pay any more for the simple stuff. But, some people just hate money…

      But I wouldn’t trust their optics.

  2. I picked one of these up after seeing it at SHOT 2023. Great for an affordable everyday carry optic on my Hellcat. After 12 hours, the dot turns off and in the morning (or whenever it’s off) you simply press the “+” button to turn it back on. They include a few sets of mounting hardware, none of which fit my Hellcat – so you’ll have to go aftermarket there.

    • Since .308 carry handles are impossible to find and purchase without getting a second mortgage my .308s have what you would call airsoft junk Ncstar detachable front and rear sights. Seeing the Ncstar glass as half full I threaded the front detachable Ncstar sight base to accept a Meprolight post, the shorty A2 style rear sights was converted to accept Trijicon 2 dot apertures and a sight tower guide pin was installed on each…No way are these mods easy to do but they are mods most all by design wiggling A2 sights require including Colt. I could have purchased DIFM nights sights and spent $100.00 a pop extra for sights that would not perform as well or look any better, etc.
      According to the author’s testing the PA stamped sight is nothing more or less than a cost saving lifetime warranted sight. Thus far from my conversations and dealings with PA they talk the talk and walk the walk.

      • 1. I’ve been through two of them. both failed. one the glass cracked at corner.

        2. The PA web site specs say it has click adjustment 1 MOA per click. This is not true, its advertised with false information. its the same cheap Chinese “turn screw and guess” and its easy to turn because the mechanism is sloppy and not made with close tolerance which is also common on airsoft area budget junk.

        3. The ones I had did not hold zero for long (10 mags) and started. shifting and had to be re-zero’d. Although the zero did not move much each time it moved when it did it moved by the same increments amount each time (which is common with the cheap airsoft level budget sights) until it was off target surface. This also indicates a loose tolerance mechanism that is common in the area of airsoft budget sights.

        it’s junk in the area of airsoft budget.

        I would not use it on a defense firearm.

        • I would not use it on a defense firearm or any of my firearms.

          the only reason I tried them out was my brother got them for free, both brand new in packaging.

          I threw them in the garbage.

        • correction for: “one the glass cracked at corner.”

          not glass cracked, the enclosure cracked at corner at the glass.

  3. hey J Dub, does the picatinny base that’s shown in one of the pictures come with the sight, or do you have to find one separately? This seems like it would be a much better value than the PLASTIC Sig dot sights.

  4. So JWT, you’re saying that this red dot was clear and didn’t bloom or flare with your astigamatism? That’s great! The only Red Dots/ Green Dots that I’ve looked through that don’t bloom or flare are the Holosuns with the ACSS reticle. I may just go ahead and get a 507c and or a 507k. But if I could find an option that doesn’t bloom or flare that is a little less expensive I might go with that. It might be worthwhile to do a review of red dots that work with those of us with astigmatism. There doesn’t seem to be anyone on the interwebs who has done that article or video. For rifle red dots I’ve gone to prism Optics . No blooming or flaring . Thanks!

  5. PA lowers and uppers = Yes.
    The rest = meh, not really.

    You can easily get a PA upper and lower, put a good BCG and barrel on them and have a high quality weapon. But optics? eh… that’s pushing it.

    Some things you just have to adopt the “buy once cry once” methodology.

  6. I have been able to break every brand of optic EXCEPT Trijicon.

    So; for competition use I usually defer to Holosun (although I’m loving the Trijicon SRO right now) but for carry I only go with Trijicon.


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