The M4S is the latest generation red dot sight issued by the U.S. Army. It is virtually identical to its predecessor, the M4, except for the location of the battery compartment. The M4 places the battery compartment on the top of the scope whereas the M4s places it down low. Both sights are available and strictly a matter of preference.

The low placement of the battery compartment allows better vision over the scope, which was the reason for the change. However, if you are using additional optics, such as the optional Aimpoint 3X multiplier or a night vision monocular, the low placement of the battery compartment (which houses the dot intensity knob) might be more difficult to get to. We prefer the M4s and didn’t find the low placement of the intensity knob to be a problem.

The intensity knob has 16 settings. Nine of these settings are visible red dots of various sizes/brightness. The remaining 7 are infrared dots to be used with night vision equipment.

A really special feature is the amazing battery life -- rated at 80,000 hours, when set to step 12 brightness. That’s over eight years from a single AA  battery. Because of this, there is  no ‘off’ switch -- it doesn’t need one.  Realistically, if you replaced the AA battery once a year as really cheap insurance, you would never have to worry about picking up your gun and the sight not working. Red dot sights of the past have always been less than ideal due to poor battery life and the auto power-down systems employed in order to get the most out of expensive lithium batteries. The convenience of a scope that uses a AA battery is phenomenal.

Lens covers and a kill flash come installed. The killflash is an anti-reflection device designed to eliminate potentially compromising reflections from the objective lens.  A slight recommendation is to replace the provided, bikini-style lens covers with Aimpoint flip covers. These are more convenient and faster to open. However, we did find that the rear one had a tendency to fall off, due to a very short surface for it to attach to. But the front flip cover was almost impossible to remove after being on for several months.

Another great feature of this sight is the integral mount, adjustable to 2 heights.  No scope rings or other devices are needed to mount this scope, making the mount very rigid and easy to align. Bumps and heavy handling are not going to move the scope in relation to the bore of the rifle.

The only downside to the integral mount is that it requires a Picatinny rail on the firearm in order to mount and standard scope rings will not work. The included mount has a large knob with pre-set torque to properly mount the sight on any standard Picatinny rail. When mounted with this mount, the dot sits above the standard GI front sight but not quite in the lower third, as preferred by many operators. We didn’t find this objectionable on our test AR-15, but you can buy an optional, high quality base, such as the LaRue LT659, to screw into the upper mounting surface. Of course, it’s not an issue if you don’t put this on a standard AR-type rifle, with standard sight.

The M4s has large optics and is very bright. It’s parallax free and doesn’t require centering. The dot covers 2 MOA (minutes of angle) which, at 100 yards, equals 2.094 inches. Most people only use 1 inch as the definition of an MOA at 100 yards. For calculating MOA at other distances or units of measure, see this page.

The scope was very easy to zero. In fact, it was already very close to zero, straight out of the box.  Accuracy and repeatability at 100 yards were excellent. We shot several thousand rounds of 5.56 ammo out of the test gun with the red dot scope and it performed as designed.

After removing the scope dozens of times, the factory mount held zero, requiring only minimal adjustments. None of the variances were beyond what might be called combat or hunting accuracy. Other than long distance target shooting, you needn’t worry about taking off the scope and re-sighting for any situation. A target shooter will zero their scope before remounting, regardless.

We’ve used this scope for over a year, in temperatures ranging from minus 30 to over 90 degrees Fahrenheit (it’s rated from minus 50 to + 160 degrees Fahrenheit !). It performed with no problems -- even in pouring rain (waterproof to 150 feet). Being a MilSpec device, it can really take a beating. We had the scope covered in mud, including the lenses. After a quick rinse and a final cleaning of the lenses with a lens pen after drying, it was as good as new.

In essence, this is likely the best scope money can buy.

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