Red dot sights

• Footprint compatibility, first and always. RMR, RMSc, Docter/Noblex, Aimpoint ACRO and Holosun K-series are all different bolt patterns. Confirm what your slide is cut for before you shop, and prefer a direct mount over an adapter plate — plates add height, add a failure point, and add recoil-loosening screws.
• Dot size is a speed/precision trade. A 6 MOA dot is faster to find and covers 6 inches at 100 yards. A 1 or 2 MOA dot is more precise and harder to pick up under stress. 3 MOA is the common compromise; many shooters with astigmatism find a larger dot reads cleaner.
• Closed emitter for duty and weather. Open emitters — the classic RMR shape — can occlude with rain, snow, lint or blood because the LED fires across an exposed gap. Closed emitters seal that path. They are bulkier and cost more.
• Battery life claims assume a low setting. A quoted 50,000-hour runtime is usually at a mid or low brightness. Daylight-bright settings drain far faster. Prefer bottom-load only if you enjoy re-zeroing; side or top load lets you swap without dismounting.
• Co-witness decision belongs to the build. Absolute co-witness puts irons in the middle of the dot window; lower-third parks them at the bottom, giving a cleaner view. Decide before you buy the mount height.
• Torque and thread locker, every time. Manufacturer torque specs on optic screws are not a suggestion. Use a proper inch-pound driver and the specified thread locker, and re-check after the first hundred rounds.

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