In early 2015, Glock introduced its Modular Optic System (MOS) Configuration pistols, where the rear of the slide has a relief cut just forward of the rear sight. This cut is fitted with a removable plate and is used to mount a miniature reflex sight to the slide.

Miniature reflex sights have become common on handguns, especially those used for competition and hunting. They have also made inroads in the law enforcement and personal- defense worlds. Well, I wanted to investigate the practicality of these new Glock MOS pistols, so I obtained a G35 Gen4 in MOS Configuration as well as an EOTech Mini Red Dot Sight (MRDS).

Fast & On Target

The Glock 35 Gen4 in MOS Configuration is a full-sized pistol with a 5.31-inch, polygonal-rifled barrel, an overall length of 8.74 inches, an unloaded weight of 27.53 ounces and a standard cartridge capacity of 15+1 rounds. Since it is a Gen4 pistol, it has a polymer frame incorporating Glock’s Multiple Backstrap System, or MBS, which is composed of interchangeable backstraps that allow the shooter to tailor the length of the grip frame and trigger reach to his or her hand. Some of the backstraps also provide a beavertail extension at the upper rear portion of the grip frame. The dust cover of the frame has an integral accessory rail for tactical lights or laser sights. Another Gen4 enhancement is the dual recoil spring assembly, which helps to tame felt recoil and ensures proper functioning even after firing thousands of rounds.

The texturing on the grip frame offers enhanced control, with raised “pebbles” along the sides, frontstrap and backstrap instead of traditional checkering. The frontstrap also has subtle finger grooves. Finally, Glock’s Gen4 pistols feature large, reversible magazine catches.

Other features of the G35 Gen4 MOS include fixed sights, with a white-dot front sight and white-outlined rear sight. The front of the slide is rounded for easier reholstering, and all of the steel parts have a non-reflective finish that’s practically impervious to corrosion. Like all other Glock pistols, the G35 Gen4 MOS features the ultra-reliable striker-fired Safe Action, and this model comes with trigger pull weight set at 5.5 pounds.

The EOTech MRDS is built to military specifications for use with USSOCOM operators. It has a tough polymer housing and comes with an optional steel shroud that can be added for extra protection. It is 1.9 inches long, 1.2 inches tall, 1.1 inches wide and weighs a mere 0.9 ounces (with the battery, sans cover). It projects a 3.5-MOA red aiming dot and automatically adjusts its intensity while offering four manual brightness settings. A rubber-covered switch at the rear of the unit activates the aiming dot and adjusts its brightness. Powered by a 3-volt CR1632 battery, the MRDS will operate continuously for a year in photodiode mode. Housings are available in black or tan.

Zeroing In

With the gun and sight in hand, it was now time to mate the two. The mounting plate that came on the G35 Gen4 in MOS Configuration is held in place by two T10 Torx screws secured with blue LocTite. Glock offers a set of mounting plates designed for popular reflex sights, and I found the #1 plate fit the MRDS well. This is the plate I mounted to the pistol’s slide before adding the sight to the plate. Four pins on the bottom of the sight fit into corresponding holes in the sight base for a firm and secure attachment.

My next step was to get the EOTech MRDS sighted-in to some degree. I thought this could best be accomplished with my Mini Bore Sight from LaserLyte. This device projects a 5-megawatt Class IIIa red laser and is powered by three 393 batteries. The device is centered in the bore using screw-on and adjustable, plastic adapters that make it work in guns from .22 to .50 caliber. With the proper adapter in place and adjusted, the Mini Bore Sight will be centered in the barrel. A rotating switch activates the laser, and I decided to sight-in the EOTech MRDS at a distance of 10 yards. The MRDS has click-adjustable screws for windage and elevation. It was a matter of activating the sight, getting the red dot lined up with the laser, and using the adjustment screws on the sight. Zeroing the sight was a snap—it took me less than a minute altogether.

Speed Demon

Now I was ready for the range. I used three brands of .40 S&W ammunition to test the Glock 35 Gen4 in MOS Configuration with the EOTech sight installed. Two were 180-grain JHP loads from Magtech and Remington. The third load was the 165-grain Gold Dot HP from Speer. I placed a large bullseye target at the 25-yard line to fine-tune the EOTech MRDS, then I loaded a magazine with the three test cartridges intermingled and fired from a bench using a sandbag rest. It didn’t take the full magazine to get the rounds hitting in the ballpark of the center aiming circle. Then I fired three 5-shot groups with each load from the same distance using the benchrest. The best five-shot group, produced with the Speer ammo, measured just 1.07 inches.

As an admitted “older dog,” I thought that the sight would not be as accurate as using the fixed sights on the pistol, but this turned out not to be the case. I can certainly see why sport shooters like reflex sights on their handguns.

I also tried the G35 Gen4 MOS with the EOTech sight on some swinging steel plate targets and found that I got very good results as far as speed and accuracy were concerned. With more practice, I believe I could really improve my shooting using this handgun/sight combination, and I think there are also a number of applications where this mating would work well for both law enforcement and self-defense uses.

For More Information

EOTech:; 888-368-4656

Glock:; 770-432-1202


  • CALIBER: .40 S&W
  • BARREL: 5.31 inches
  • OA LENGTH: 8.74 inches
  • WEIGHT: 27.53 ounces (empty)
  • GRIP: Polymer
  • SIGHTS: Fixed
  • ACTION: Safe Action
  • FINISH: Matte black
  • CAPACITY: 15+1
  • MSRP: $840

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