Primary Arms GLx MD-21s ACSS CQB by Primary Arms - $229.99 | 2026 Review

Compatibility Tags

interface: picatinny-topsuitable-for: ultra-compactoptic-type: reflexoptic: aimpoint-micro

Overview

The GLx MD-21s is the solar-equipped member of the MD-21 pair. Its top-mounted panel backs up the CR2032, while AutoLive wakes the reticle on motion and a low-battery indicator warns before the coin cell is exhausted. The 20mm aperture, 5.0 oz weight, and 2.8 inch length match the SLx MD-21, so the solar failsafe is the functional hardware difference between them.

Push buttons control 12 brightness settings, including three for night vision, and switch the ACSS CQB between four modes. Hold either button for three seconds to cycle among all features, chevron plus BDC, chevron plus horseshoe, and chevron alone. This lets the same open horseshoe, precision chevron, and three-dot drop ladder serve close work or present a cleaner aiming picture without changing the optic's zero.

Each click moves 0.5 MOA, and the optic provides 100 MOA of elevation plus 100 MOA of windage travel, nearly twice the published adjustment range of the MD-25 Gen 2. The cast, IP67, fog-resistant housing adds a fully multi-coated anti-reflective lens. Its low mount and absolute cowitness mount with spacer provide 1.41 and 1.535 inch center heights on the standard microdot footprint.

Key Features

ACSS CQB Multi-Reticle Select with four user-selectable modes
Top-mounted solar failsafe backs up the CR2032 battery
12 brightness settings, including 3 night vision settings
AutoLive, low-battery indicator, and high/low setting indicator
0.5 MOA clicks with 100 MOA of windage and elevation travel
Low mount and absolute cowitness mount with spacer included
IP67, fog-resistant cast housing with fully multi-coated anti-reflective lens

Detailed Specifications

Reticle: Red ACSS CQB Multi-Reticle Select: all features, chevron plus BDC, chevron plus horseshoe, or chevron alone
reticleControls: Hold the plus or minus button for three seconds to cycle reticle modes
reticleSubtensions: Chevron outer tip span is approximately 5.7 MOA, inner tip span is approximately 4.3 MOA, and BDC dot diameter is approximately 1 MOA, derived from the manual's ranging references; no horseshoe MOA value is published
bdcCalibration: Six references from top to bottom are chevron tip, outer wing tips, bottom legs, then BDC dots 1, 2, and 3. Yardages: 5.56/5.45 with 100 yd zero, 100/200/300/400/500/600; .308, 6.5 Grendel, or 77gr 5.56 with 50 yd zero, 50/200/300/400/500/600; 300 BLK or 7.62x39 supersonic with 100 yd zero, 100/200/250/300/400/450; 300 BLK 200gr SMK subsonic with 50 yd zero, 50/no reference/75/100/125/150; 12 gauge 1 oz slug with 25 yd zero, 25/50/75/100/125/150; .22LR 40gr with 50 yd zero, 50/no reference/100/125/150/175; 7.62x54R zeroed 1/2 inch below point of impact at 100 yd, 100/200/300/400/500/600; 9mm carbine 115/124gr with 25 yd zero, 25/no reference/100/150/175/200; 10.5 inch 5.56 with 100 yd zero, 100/200/250/300/400/500. Load and barrel length variation may require tuning with the top BDC dot at extended distance
rangingAndWind: Chevron outer tips range an 18 inch target at 300 yards, inner tips range it at 400 yards, chevron edges mark 5 MPH wind holds for 400, 500, and 600 yards, and each BDC dot covers a 5 inch target at 500 yards. Vertical ranging for a 5 ft 10 in standing target uses the lowest BDC dot and marks 500, 600, and 0 to 400 yard bands, best used behind a magnifier
shotgunReference: Horseshoe approximates the pattern of 12 gauge 00 buckshot from an 18.5 to 20 inch barrel at 25 yards
reticleManual: https://www.primaryarms.com/core/media/media.nl?id=26414765&c=3901023&h=E9lETBsNOYq8tK2CQiOeTxTKFkMBIeIdG814ktZsso-XYuRT
Magnification: 1x
Battery Type: CR2032 3V lithium coin with top-mounted solar failsafe backup
brightnessSettings: 12 levels, including 3 night vision settings
activation: AutoLive motion-activated illumination
indicators: Low-battery and high/low setting indicators
Waterproof Rating: IP67
fogResistance: Fog resistant
lensCoating: Fully multi-coated anti-reflective lens
weight: 5.0 oz
Length: 2.8 in
windowSize: 20mm clear aperture
Adjustment Type: 0.5 MOA per click
Adjustment Range: 100 MOA elevation / 100 MOA windage
Material: Cast housing
Mount Type: Standard microdot footprint
includedMountHeights: 1.41 in and 1.535 in center heights
color: Black
sku: PA-GLX-MD-21S-ACSS
mpn: 810026
warranty: Lifetime