Meprolight M21D4 M-21 Reflex Sight, 1x30mm, 4.3 MOA, Unlimited Eye Relief, Black

The Meprolight M21D4 reflex sight is a battle-proven 1x30mm optic built around a simple, powerful idea: your aiming device should work when you need it, no excuses. Trusted by military and law enforcement worldwide, this self-illuminated red dot sight runs on zero batteries and zero switches—fiber optics power the reticle in daylight, while a built-in tritium source keeps it glowing at night. It's the kind of reliability that comes from decades of real-world use in demanding conditions, not lab promises.

The large 30mm lens gives you a wide field of view and lets you shoot with both eyes open, which means better situational awareness and faster target transitions in close-quarters scenarios. The 4.3 MOA dot strikes a balance between precision and speed—fine enough for accurate shooting but bold enough to grab your eye instantly when it matters. Whether you're running it on a rifle, carbine, or shotgun platform, the unlimited eye relief means you'll never chase your sight picture; you get a full sight picture from nearly any shooting position, and the 114mm profile stays compact on your gun.

Built to mil-spec durability, the M21D4 is sealed, shockproof, and designed to function across extreme temperatures and harsh field conditions. No switches means no accidental shutdowns; no batteries means no dead sights in a firefight. If you run a duty rifle, home-defense gun, or tactical carbine and you value simplicity and reliability over trendy features, this is a sight that earns its place on your rail.

Key Features

• Self-illuminated day/night operation—fiber optics and tritium, no battery required
• Large 30mm objective window for wide field of view and both-eyes-open shooting
• 4.3 MOA illuminated dot for rapid target acquisition and precision
• Unlimited eye relief—works from contact distance to extended range
• Military-grade durability: shockproof, sealed against the elements
• Compact 114mm length, lightweight at 372g with Picatinny adapter
• No switches, no moving parts—always ready for action

Specifications

Frequently Asked Questions

Do I need batteries to run the Meprolight M21D4?

No. The M21D4 is fully self-illuminated using fiber optics during the day and a built-in tritium source at night. There are no batteries, switches, or external power sources required. This design ensures the sight is always ready to use without worrying about power loss in the field.

What's the difference between unlimited eye relief and the listed 10mm to 600mm spec?

The 10mm to 600mm range represents the distances at which you'll see a sharp sight picture. "Unlimited eye relief" means there's no critical eye-box constraint—you can shoot comfortably from almost any head position and still see the full reticle, which is crucial for fast, instinctive shooting in close quarters or tactical situations.

Will the M21D4 work on an AR-15 or other Picatinny rail?

Yes, the M21D4 comes with a Picatinny adapter and is designed to mount on any standard Picatinny rail found on rifles, carbines, and tactical shotguns. The compact 114mm length makes it well-suited for modern modular platforms.

How long does the tritium stay bright?

Tritium has a half-life of about 12 years, meaning it will remain functional well beyond that period but will gradually dim over decades. For practical purposes, you'll have reliable night illumination for the life of the optic under normal use.