Primary Arms sent me the SLx MD-21 for evaluation, a forged T2 pattern red dot that comes in under $200.
Seems like only fifteen years ago, anything beyond irons meant spending rifle money on an optic.
Now the market’s flooded with glass at every price point, and Primary Arms has carved a niche by offering feature-rich options that stay affordable.
The MD-21 features a 2-MOA dot, twelve brightness settings, and AutoLive motion activation. Instead of traditional capped turrets, it uses recessed exposed adjustments set into the forged housing.
The 21 mm objective is only a millimeter larger than the traditional micro dots, but that extra space and a sleeker housing make the window feel noticeably less cramped.
At 3.8 oz bare, it’s 0.2 oz heavier than a Vortex Crossfire II. ACOG owners will know what I mean; nothing beats the feel of a dense, forged housing in hand.
The T2 footprint means the sky’s the limit for mounting options. Primary Arms includes an absolute co-witness mount, a 1/3 co-witness mount, and even a shim plate for fine-tuning height and fitment.
I chose to run it as a 12 o’clock red dot on my SLx 1-6 Nova. Matching optics just look right, and the MD-21’s window sits lower in its footprint than comparable Holosun or Vortex models.
In a sea of positives, brightness is its Achilles’ heel. Even at max setting, the dot struggles in daylight. The attached photo was taken in the shade at full brightness, and to my eye, it was barely visible.
Not being daylight bright, paired with a slightly larger footprint and extra weight, keeps the MD-21 on top dot duty. It feels rugged, well-built, and affordable, but brightness could make or break whether this one earns a permanent slot on your rifle.
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