M1 BullPup’s REM 21 Light Upgrade for Meprolight M21 Sights…and More

Last year I built an IDF Israeli Menusar, sometimes referred to as the Mekut’zar carbine clone. Since then I’ve done a few updates to it including adding a FAB Defense mag carrier, and swapping out the grip to a B5 Systems CAR15 LS2-Shiny.

The biggest change though was that I managed to snag an IDF surplus Meprolight M21 from a guy on one of the gun forums. I picked up a gooseneck mount from Meprolight for it and was good to go. The only issue was that these sights had been well loved and the Tritium was pretty dim. I knew that going in, but figured I’d live with it. Luckily someone on another gun board clued me in to M1 BullPup and their LED light upgrades for the M21.

The REM 21 and REM ACOG

The REM 21 reticle enhancement module fixes the problem that is inherent in the Mepro 21 sight. In certain low light conditions, or when aiming at bright or light colored backgrounds, the Mepro 21 loses its sight picture. That can be an issue on new optics, let alone one like mine that’s old and well used, with the tritium at the end of its life span.

The M21 also has fiber optic capability, but even using that in daylight can be impacted by light conditions and what background you’re shooting against. With the REM 21 installed, if that happens all you have to so is turn on the REM 21 and you get a sharp sight picture.

M1 BullPup’s REM 21 is a bolt-on battery powered LED light designed to illuminate the fiber optics of the M21 sight. When you lose your reticle, just turn on the REM 21 and the reticle looks like it’s in bright sunlight. There’s a side mounted knob with 11 brightness settings. This lets you adjust the brightness to whatever level you need from dim indoor light to bright mid-day sunlight outdoors. If the tritium in your sight is still good, the REM 21 doesn’t interfere with that, and it will still work normally.

The REM 21 comes in a clam shell package and ships with the REM, a battery, a new screw and Allen wrench, and an instruction sheet. Cost is just $36.95 with free shipping in the US. There are a few different variations of the Meprolight M21 take a good look at the options when you order your REM 21 to be sure you choose the right one.

Installation is extremely simple. Just follow the instructions, but essentially you remove one screw from the side plate on your M21, snap the REM 21 module in place, and secure with the longer screw provided in the kit. It takes a couple of minutes at most. Mounting is solid and while it adds a minimal amount of bulk to the sight, the weight is negligible.

With the REM 21 installed you can choose to use it or not. If the lighting conditions are good and you don’t need it, just use your M21 as usual. If you find yourself having trouble seeing the reticle, though, just turn the to whatever illumination setting works for your current conditions. When you’re done shooting, tun it off. It doesn’t have any fancy features like shake awake or auto off, but it’s easy and straightforward to use.

Battery Life

The REM 21 uses a common CR2032 3-volt battery, which is included with the kit. Battery life is 106 hours of continuous use. That isn’t nearly as long as many modern dedicated red dots, but this is designed to supplement your optic’s existing system when needed. Plus it’s a lot less expensive.

The specs say you can optionally use two CR2016 batteries instead and get an even brighter sight picture, but I haven’t tried that option yet.

But Wait, there’s More…The REM 22

M1 BullPup doesn’t just offer REMs for the Meprolight M21. They also have a new version for the Mepro M22 as well. Meprolight makes a light module kit for the M22, but it’s $125. The REM 22 from M1 BullPup is only $36.95 shipped. The Meprolight kit has an auto shut-off feature, but you’re paying about $90 more to get that. Also, the Meprolight light kit has three illumination levels, while the M22 REM has 11, just like the REM 21.

Unlike the REM 21, the REM 22 needs to be installed by the folks at M1 BullPup. When you order, you’ll need to send your side plate in for them to do the installation, then they’ll ship it back so you to put back on your sight. The REM 22 units are still pretty new, so they aren’t listed on the M1 BullPup website yet. If you need one, you can order a REM 21, and then put in the notes section when you order that you need it for a REM 22.

The REM ACOG

Last but not least is the REM ACOG. Just as the REM 21 upgrades the Meprolight M21, the REM ACOG enhances the performance of Trijicon’s ACOG sights. The REM ACOG illuminates the reticle of the Trijicon ACOG TA31/M150 sight in low light conditions.

That’s not all it does. though. It also reduces the reticle “bloom” in bright daylight. Have you ever seen ACOGs with tape or some other covering over most of the fiber optic rod? That’s because they’re trying to minimize the bloom issue of the sight being too bright during the daytime.

The REM ACOG is designed to cover half of the sight’s fiber optic to reduce that reticle bloom without resorting to tape. The REM ACOG also eliminates the need for the trick of taping a chem light to your ACOG to fuel the fiber optics at night. The REM ACOG is designed so that you can still use the Trijicon TA91 Tennebrex Killflash Anti-Reflection Device too.

Like the other REM units, the REM ACOG illuminates the light collector fiber optic on the sight when you need it and has 11 brightness settings. The reticle can be seen in total darkness on the lowest setting or when aiming from a dark room out into bright sunlight on its highest setting. Like the REM 21. the REM ACOG doesn’t interfere with the Tritium illumination of the sight either.

The REM ACOG fits the standard TA51 Flattop mount, although it can be adjusted to fit any other mount as well. You just have to note what mount you have when you order. If you’re concerned about the durability of the module, M1 BullPup says that they’re water proof and dust proof and have been tested from 0 degrees Fahrenheit to 120 degrees Fahrenheit.  It’s made from a 30% glass filled Polymer, the same stuff used in AR pistol grips and hand guards.

The REM ACOG is powered by a single CR2032, 3-volt battery, which is included. It has a battery life is 390 hours of continuous use. Weight is just 2.5 ounces. MSRP on the ACOG module is $44.95 with free shipping within the US.

Installation

The REM ACOG is a two-piece clamshell design that goes around the ACOG sight body. I didn’t own an ACOG, but I borrowed one to try out with the REM ACOG unit. It might have taken a little longer than installing the REM 21, but it was still a simple prospect and was done in a few minutes. You just need to line up the two sides on the unit and secure it with the two provided screws. Once it’s installed, it’s solid with no movement or play of any sort.

Operation is just like the REM 21. You have a side-mounted knob with 11 brightness settings. When you run into a situation where the light or backdrop is washing out the reticle, simply turn the knob to a level where you can comfortably see the reticle again.

The ACOG I borrowed was in good shape with good tritium so it wasn’t as tired as my M21. Still, in testing there were times when the REM ACOG unit came in handy. The partial cover of the fiber optic did, in fact, help with the bloom effect as well. It’s a pretty inexpensive upgrade for a sight that you’ve invested a lot in already and it’s more elegant than slapping tape onto it.

Whichever REM Fits

Whether you have an old sight like I do that needs a bit of a boost, or just want to make the most out of your new site, the Reticle Enhancement Modules from M1 BullPup are worth a look. They’re extremely affordable, simple to use, and work well. They’re American designed and made niche products that enhance and extend the lifespan of some great rifle optics like the Meprolight M21 and M22, and the Trijicon ACOG.