The Mepro M21 non-magnifying reflex sight from Meprolight is powered by a fiber-optic collector and a tritium gas tube that illuminate its reticle during daylight and night time, respectively, and that are self-regulating for brightness. That means that, unlike most reflex sights on the market, the M21does not require batteries and is devoid of external wires and switches, enhancing its general durability and water-resistance characteristics.
Developed in conjunction with the Israeli military for use on its Tavor bullpup rifle the Mepro 21 has been tested in combat since its development in 2002. Not surprisingly, then, our test sample immediately conveyed the appearance and feel of a no-nonsense, well-built piece of optical gear. Its one-piece aluminum alloy housing and flush-mounted adjustment knobs, which exhibit tactile clicks when their slots are turned with a coin or cartridge rim, make its exterior durable and snag-free. And its 41/2-inch length takes up minimal space-approximately 12 slots-on a standard Picatinny rail.
Our unit came equipped with a double throw-lever mount, held neatly to the its underside with large Torx-head machine screws, making attachment and detachment from the two different 5.56x45 mm NATO flat-top rifles used to test it-an IWI Tavor SAR and an AR-15-quick and repeatable. Other adapters, such as one for an AR carry handle, are available. Our Mepro 21 also featured the “bullseye” reticle, consisting of a four-section outer ring surrounding a dot. Again, several other designs are available depending on user preferences and needs. Reticle height is approximately 1.65 inches, or 42 mm, above the rail’s top surface.
We fired several kinds of ammunition from both an indoor bench and from various positions in the field in a wide range of temperatures, detaching and remounting the M21 several times. It not only acceptably returned to zero, it also properly “shot the square,” although several users noted that its adjustments were rather coarse at 1 m.o.a. per click. Despite that fact, we were able to produce groups consistent with the sight's intended CQB application using its 4.3-m.o.a. center dot. In a variety of lighting conditions ranging from dimly lit rooms to snow-covered landscapes, the orange-tinted reticle proved bright and sharply defined with only one significant instance of “washout” occurring as it was aimed from inside a shaded position onto a snow-covered field. Even then, the bullseye was faintly visible and proper aiming could still be accomplished when specifically targeting somewhat darker objects.
The Meprolight M21 is competitively priced when compared with other military-grade reflex sights, and it offers the advantages of automatic brightness control and battery-free operation. It is ideally suited for modern, lightweight semi-automatic self-defense rifles, which may need to be called into action on a moment’s notice when the lack of necessity to “activate” a sight or replace depleted batteries could prove a critical advantage.