Primary Arms MD‑21 Red Dot Test | Solar vs Standard Options

Published on December 14, 2025
Duration: 9:40

Elliott Delp and Sparky review the Primary Arms MD-21 (SLx) and MD-21S (GLx) red dot sights. The GLx model offers a solar option and advanced ACSS reticle configurations for an additional $40-$50 over the SLx model, which features a standard 2 MOA dot. Both optics are praised for their value and feature a 2 MOA dot, 12 illumination settings, and Aimpoint Micro footprint.

Quick Summary

The Primary Arms MD-21S (GLx) red dot sight is recommended over the MD-21 (SLx) due to its integrated solar panel for extended battery life and the versatile ACSS-CQB reticle system, which offers multiple aiming options.

Chapters

  1. 00:00Introduction: MD-21 & MD-21S Overview
  2. 01:57GLx vs SLx: Key Feature Differences
  3. 03:37Technical Specifications: Dot, Illumination, Starburst
  4. 04:10ACSS Reticle System Explained
  5. 05:57Adjustments, Battery Life, and Auto-Off
  6. 06:51Mounting Options and Footprint Compatibility
  7. 08:34Final Verdict and Recommendation

Frequently Asked Questions

What are the main differences between the Primary Arms MD-21 (SLx) and MD-21S (GLx) red dot sights?

The MD-21S (GLx) includes a solar panel for extended battery life and features the advanced ACSS-CQB reticle system. The MD-21 (SLx) is a more basic model without solar power and typically features a standard 2 MOA dot reticle.

What reticle options are available on the Primary Arms MD-21S (GLx)?

The MD-21S (GLx) utilizes the ACSS-CQB reticle system, which can be configured with a chevron only, chevron with BDC, chevron with horseshoe, or all features active, offering versatile aiming points.

What is the battery life and type for the Primary Arms MD-21 red dot sights?

Both models use a CR2032 battery. The MD-21S (GLx) benefits from its solar panel, significantly extending operational time. Specific battery life without solar assistance is not detailed but is expected to be substantial given the 12 illumination settings and auto-shutoff.

Do the Primary Arms MD-21 red dots have night vision compatibility?

Yes, both the MD-21 (SLx) and MD-21S (GLx) red dot sights offer 12 illumination settings, including 3 specifically designed for compatibility with night vision devices.

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