GLOCK has continued its innovative legacy by breaking new ground: adapting its Modular Optic System (MOS) to service-sized GLOCKs, an option heretofore only available through expensive custom gunsmithing. Before I describe the new offerings in the GLOCK family, a small history lesson is appropriate to illustrate how this technological leap has come about.

Getting On Target

For centuries, shooters have searched for and created various means of pointing/aiming their firearms. It’s quite possible that the first sight was a metal bead located on top of the barrel near the muzzle. Pictures of some antique Japanese matchlocks show a blade front sight and some sort of rear sight combination. Early revolvers had a notch cut into the hammer so that the front sight could be centered when the hammer was cocked. Bat Masterson, a famous lawman and gunfighter of the Old West, was known to have ordered at least two revolvers with a “front sight a little higher and thicker than the ordinary pistol.” William E. Fairbairn, a British soldier and pioneer of combat pistol training for the Shanghai Police, specified a German silver bead for a front sight on his service pistol.

Throughout most of the 20th century, various beads, blades and inserts found their way onto handguns, with the most visible having fiber-optic inserts or radioactive elements that would glow in low light. Action shooting competitors then began using low (or no) magnification optical sights, or scopes. Elite military operators began to experiment with these and electronic sights, first on long arms and then on pistols. The culmination of all of this were miniature reflex sights mounted to the slides of pistols.

GLOCK dove into this concept after careful study and engineering by offering its MOS system, first on competition pistols and now on the full-sized GLOCK 17 Gen4 and the compact GLOCK 19 Gen4. This offering is truly another paradigm shift by GLOCK, the most popular and respected pistol-maker in the world.

Modern Classics

The G17 and G19 need little introduction here. In their various iterations over generations, these pistols have served military operators, law enforcement officers and qualified civilians superbly. The G17 Gen4 MOS and G19 Gen4 MOS have nearly identical specifications to their older siblings.

They have the same time-honored qualities of earlier generations, including GLOCK’s SAFE ACTION system, now imitated but never duplicated. A polymer frame, now in GLOCK’s renowned Gen4 styling, surrounds this action. Other enhancements include an enlarged and reversible magazine catch, and all of the major metal components—including the slide and barrel—are given GLOCK’s surface-hardened, non-reflective and corrosion-resistant finish.

The slides for the G17 Gen4 MOS and G19 Gen4 MOS have cutouts between the ejection port and rear sight for mounting today’s most popular miniature reflex sights. Because of incredibly precise computer-controlled machining, you’ll barely be able to notice this cutout’s cover plate when viewed from the side. From above you’ll see the flush, unobtrusive mounting screws that secure the cover plate. After loosening them and removing the cover plate with the supplied wrench, you can select the proper mounting plate for your reflex sight and install it onto the slide. It’s simple and fast.

Easy Aiming

The proof is in the shooting, clearly, and I asked GLOCK Sport Shooting Foundation (GSSF) Rangemaster Justin Hixon to join me at the indoor range at the GLOCK training facility in Smyrna, Georgia, to put the G17 Gen4 MOS and G19 Gen4 MOS through their paces. Justin recently began competing in a number of action shooting disciplines, including GSSF matches, and I knew he would bring a fresh perspective to the versatile new products.

We shot both pistols from static standing positions and while moving diagonally across the targets. Both the G17 Gen4 MOS and G19 Gen4 MOS had Leupold DeltaPoint Pro reflex sights installed. Other popular options on the market include the Trijicon RMR, the Burris FastFire and the C-More STS, all quick-targeting single-lens reflex sights.

With reflex sights, you shoot with both eyes open. Essentially, the operator looks at the target, brings the sight to eye level and superimposes the (usually) red-dot reticle over the target. Assuming the sight has been adjusted correctly, proper trigger manipulation will result in a hit on the target.

After a bit of shooting, Justin was impressed by the pistols’ fast target acquisitions and enhanced accuracy potentials. We tested the pistols for accuracy and, at 15 yards and beyond, came close to having all rounds creating one ragged hole in the test targets. Subjectively, I found it easier to focus on the target and concentrate on manipulating the trigger. Shooting at targets while moving was also much easier—quick and accurate shots were the norm. I didn’t have to transition my focus back and forth between the targets and sights. Now it was easy for me to look at the target, put the reflex sight’s reticle on the target and carefully work the trigger.

This GLOCK development has serious implications in a number of areas other than competition and target shooting. The ability to keep both eyes open while shooting could be an invaluable lifesaver, no matter who the operator is. And mounting the sight on the slide keeps the pistol compact and holster compatible. Expert shooters and beginners alike will surely appreciate the aiming assistance. These new GLOCKs are a hit—and they’re sure to hit whatever targets they are aimed at!

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  • Caliber: 9×19
  • Barrel: 4.49 inches
  • OA Length: 7.95 inches
  • Weight: 24.87 ounces (empty)
  • Grip: Polymer
  • Sights: Fixed
  • Action: SAFE ACTION
  • Finish: Matte black
  • Capacity: 17+1
  • MSRP: $726

GLOCK 19 GEN4 MOS Caliber: 9×19

  • Barrel: 4.02 inches
  • OA Length: 7.28 inches
  • Weight: 23.63 ounces (empty)
  • Grip: Polymer
  • Sights: Fixed
  • Action: SAFE ACTION
  • Finish: Matte black
  • Capacity: 15+1
  • MSRP: $726

This article was published in the GLOCK AUTOPISTOLS 2016 magazine. To see the rest of the issue, please visit

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