Best Red Dot Sights for Glock 43X & 48 MOS: Why Direct Mount Wins

If you own a Glock 43X MOS or Glock 48 MOS, you probably bought it for one reason: it’s slim, concealable, and optic-ready. And if you own any other Glock Slimline MOS pistol, this guide is for you too. The G43, G43X, and G48 all share the same RMSc footprint, so everything here applies across the board.

Here’s the catch most new owners don’t know about. The most popular micro red dots out there, like the Holosun 407k and 507k, do not fit directly onto your slide. You need either a bulky adapter plate or a permanent modification to make them work.

The right answer is a Direct Mount optic. Our top pick is the Swampfox Sentinel II, which bolts straight to the factory slide cut. No plates, no grinding, no headaches.

Glock slaps the “MOS” label on all their optic-ready pistols, but that name is doing a lot of heavy lifting. Depending on which gun you have, the footprint underneath is completely different.

Standard MOS (G19, G17): Uses a giant cut designed for adapter plates.

Slimline MOS (G43X, G48): Uses the RMSc Footprint.

The Slimline MOS cut has four recoil lugs (two front, two rear) plus a specific screw pattern. That’s where things get complicated. A lot of popular optics, like the Holosun K-series, use a “modified” RMSc footprint that skips the rear lug holes entirely.

So if you want to run one of those optics, you’re stuck choosing between two bad options:

Buy an Adapter Plate: It lifts the optic 2-3mm off the slide, and that extra height is usually enough to kill any chance of co-witnessing your irons.

File Your Slide: You grind the rear lugs off your Glock slide. That’s a permanent modification on a gun you paid good money for, and it voids your warranty on the spot.

There is a better way.

The Swampfox Sentinel II was built from the ground up for the RMSc footprint on the Glock 43X, 48, and 43 MOS. It has recesses for all four recoil lugs, so it drops onto the slide and locks in solid, no plate required.

1. True Co-Witness

Without a plate stacking height underneath it, the Sentinel II rides low on the slide. Low enough that your factory standard-height iron sights show through the bottom of the window. Battery dies at the worst possible moment? You’re still in the fight.

2. Durability

Every adapter plate is a failure point waiting to happen. More screws means more things that can vibrate loose under recoil. Direct mounting cuts out that risk entirely. The Sentinel II transfers recoil force straight into the slide’s lugs, not through a stack of hardware.

3. Concealability

These guns were designed to disappear under a shirt. Every extra millimeter of height is working against you. A plate-mounted optic makes the gun taller and more likely to print. A direct-mount keeps the whole setup as slim as Glock built it.

Mounting the Sentinel II takes about five minutes. Here’s how it goes:

1. Clear the Weapon: Visually and physically inspect the chamber.

2. Remove the Cover Plate: Pop off the black plastic cover plate using the Torx wrench Glock includes in the box.

3. Test Fit: Set the Sentinel II into the cut. It should sit dead flat with zero wobble.

4. Install Screws: Use the M4x0.7 screws provided in the Swampfox box. (Note: The screws that come with the Glock are for the cover plate and are too short.)

5. Torque: Tighten to 15 in-lbs. A dab of Blue Loctite on each screw is worth the extra 30 seconds.

6. Zero: Get to the range. The Sentinel II runs 3 MOA clicks, so dialing it in is quick.

The Glock 43X MOS is one of the best carry guns money can buy. Don’t give up what makes it great by bolting on a plate that raises your optic and adds unnecessary hardware. Get the right optic for the footprint, mount it clean, and carry with confidence.