The Mepro M21 is my favorite combat optic. It is built like a tank (by the same company that builds sighting systems for Merkava tanks) does not require batteries, and is impervious to water, cold, etc. Internal components are threaded in, so thermal cycling of the weapon (getting hot and then cooling) does not cause things like lenses to come loose when glue fails, as is the case with other optics.
Bill Alexander told me, “People ask me why I have a Meprolight on top of my rifle. I tell them, ‘You would’t believe the optics I have broken with the Beowulf.'” (He shoots a LOT in testing loads.)
The Meprolight M21 is the standard issue optic for the IDF. Everywhere in Israel old, battered M21s can be seen on top of rifles, often devoid of finish and missing small chunks, but still serving well. This is a testament to the ruggedness of these optics.
The Illumination of the M21 is powered by ambient light through a fiber optic collector system, automatically adjusting the brightness to ambient light levels. In total darkness, illumination is provided by a tritium light source. It is night vision compatible. The M21 has no electronics and no batteries. There is no on/off switch. The Mepro M21 is always on. Mount it on the rifle, zero, and it will be ready to go anytime you pick the rifle up. There is nothing to die, nothing to forget, nothing to bump.
Zero adjustments take place between the sight itself and the mount. This makes the adjustment mechanism much more robust than the delicate adjustment systems that are internal in most sights.
The most common mounts are a quick-release Picatinny rail mount and a carry handle mount.
The carry handle mount attaches to an M16 or AR-15 carry handle and places the sight just over the handguards in front of the carry handle. This is the most common way the IDF mounts an M21 on a carry-handle M16.
If the rifle or carbine happens to have a rail system like the NFR, the quick-release mount can be used to mount the sight to the top rail of the handguard. The M21 is designed to work this way with the reticle visible over the top of the carry handle.
For a flat-top upper, get the Mepro M21 with quick-release mount. It is not uncommon in the IDF for M21s to be mounted forward on the top rail of a rail system (instead of on top of the upper) in special ops units. The QR mount can be tightened or loosened by adjusting the nuts opposite the levers. This is especially handy in the US where commercial rifles often vary quite a bit in the width of the top rail. If you do not want the QR option, the nuts can be tightened up until the levers cannot be opened. Some US law enforcement agencies require this as they have found that officers often sit in their patrol cars and flip any accessible QR mounts open and closed all day.
The M21 has several available reticles. They are:
The dot reticles come in two sizes and are probably the most common reticle in use by the IDF. The smaller dot gives better precision, but can be harder to acquire in certain light conditions. The larger dot is faster to acquire, but gives less precision.
The Bullseye reticle is probably the best reticle for close-in CQB fighting. The reticle is a dot surrounded by a broken circle. It is very quick to pick up and at close range can serve as a giant dot. On very small or distant targets, the reticle can obscure the point of aim, somewhat.
The triangle reticle is the best of both worlds. It is easy to find and is used as a large dot when quickly engaging close targets, but the tip of the triangle can be used as a precise aiming point for smaller or more distant targets.
The Open X reticle was designed for use with magnifiers. It can be used as a large dot at close range, but for longer shots when using a magnifier the point of impact is unobscured for more precise shot placement.
The Meprolight M21 is the correct optic for most IDF carbine builds. Like the IDF carbine itself, the M21 is the embodiment of rugged simplicity. For most carry-handle builds, the Mepro M21 with carry handle mount is most appropriate. For a carry handle carbine with an NFR rail system, the carry handle mount Mepro M21 can be used, or the quick-release Picatinny rail mount can be used to mount the sight to the top rail in front of the carry handle.
For a flat-top build, the Mepro M21 with QR mount should be used and can be mounted to the top of the receiver, or in the case of a rifle with a rail system like the NFR or VFR, can be mounted forward on the handguard. If you happen to find an older M21 with the one tall side fiber optic window on each side, and are brave enough, you could break off one side of the body in front of the window for the ultimate in authenticity. (This happened sometimes to the older sights after a lot of rough use. The current split window fixes this.)