Primary Arms SLx MD-21
The Primary Arms SLx MD-21 is a red dot rifle optic at 1x magnification, using a 2 MOA aiming point in red. It ships on a fixed mount at Absolute Co-Witness or Lower 1/3 height (1.41 or 1.535 in optical centerline). It runs on a CR2032 cell and adds shake awake and night vision settings. The aluminum body weighs 5 oz. Measured against the 320 red dots and prisms in the index, it lands in the lightest quarter for weight (5 oz) and among the least expensive 10 percent for price ($180). It is one of 149 entries in the index that qualify as a red dot at 1x. The closest listed comparison is Primary Arms SLx MD-25 Gen II, the same brand's red dot at 1x, priced at $180.
| Series | SLx MD-21 |
| Optic Type | Red Dot |
| Magnification | 1 |
| Reticle Color | Red |
| Reticle Size (MOA) | 2 |
| Solar Failsafe | No |
| Shake Awake | Yes |
| Night Vision Compatible | Yes |
| Enclosed | No |
| Battery | CR2032 |
| Optic Removal for Battery Change | No |
| Mount Type | Fixed |
| Mount Height | Absolute Co-Witness / Lower 1/3 |
| Mount Height (in) | 1.41 / 1.535 |
| Material | Aluminum |
| Weight (oz) | 5 |
| Average Price | $180 |
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