The Glock 43X and Glock 48 MOS pistols only accept RMSc-footprint optics, which makes the optic-selection problem narrower and cleaner than full-size Glock work. This isn't a 50-option category like the Glock 17 or Glock 19 lineup — the right pick comes down to glass quality, dot crispness, whether the emitter is open or enclosed, and whether you want a circle-dot reticle or a clean dot. The RMSc shelf turns over quickly, so this update rebuilds the picks around what is actually on the shelf at 3CR Tactical right now.
What "RMSc Footprint" Actually Means for the 43X and 48
Both the Glock 43X MOS and Glock 48 MOS ship with a slide cut for the RMSc footprint — narrow screw centerline, specific lug geometry, designed to fit on a subcompact-width slide that has no room for a wider RMR-pattern optic. The 43X and 48 use the same slide width and the same MOS cut geometry, so anything that bolts to one bolts to the other.
RMSc, Holosun K, and J-Point all share that footprint. Listings that say "RMSc / J-Point / Holosun K" all mean the same hole pattern, so an optic sold under any of those names lands on the same cut without a plate. The Trijicon RMRcc is similar in size and intent but uses its own screw and lug pattern — it is not interchangeable with RMSc, and that distinction matters more than any spec on the box.
Open vs Enclosed Emitter
When this guide first ran, enclosed-emitter optics in the RMSc size class were rare and expensive. That has changed, and it is now the first question worth answering.
An open emitter puts the LED in an exposed channel facing the lens. It is lighter, cheaper and sits lower, and it is the easier optic to co-witness with standard-height irons. The failure mode is debris: pocket lint, rain or snow across the emitter window and the dot washes out. An enclosed emitter seals the LED behind a second lens — you pay in height, weight and price, and gain a dot that keeps working after the gun has ridden in a waistband all summer. For a dedicated carry Glock 43X or Glock 48, enclosed is the more defensible choice; for a range gun, an open emitter saves money and bulk. Either way, keep the optic proportionate: a Glock 43X is light to start with, and an oversized sight changes both the balance and the holsters you can use.
Two of the picks below are true enclosed-emitter designs on the RMSc pattern — the Viridian RFX42 and the OSight SE. The rest are open-emitter optics, which is still the right answer for a range gun or a lightly carried pistol.
The Picks
Viridian RFX42 — Best Enclosed Emitter for a Slim Slide
The Viridian RFX42 is an enclosed-emitter micro on the RMSc footprint with a 3.5 MOA green dot, and it is the pick for a carried Glock 43X or Glock 48. The sealed housing keeps lint and weather off the LED, which is the whole point of an enclosed design on a carry gun, and the body is small enough that it does not fight the slim slide profile the way a full-size enclosed optic does — it is one of the smallest fully-enclosed RMSc dots made.
Green reads brighter to most eyes at the same power draw, which is why the battery figure holds up at roughly 28,000 hours despite the enclosed housing. Ten brightness settings including two night-vision levels, Instant-On motion activation, and a CNC-machined aluminum body round it out.
OSight K and OSight SE — The Entry Point
These are the two least expensive ways into a quality RMSc dot on the shelf right now. The OSight SE is the enclosed-emitter model, running a 2 MOA dot with a 32 MOA circle in a multi-reticle setup. Getting an enclosed emitter and a circle-dot reticle at this tier is unusual, and for a first red dot on a Glock 43X it is the easiest recommendation in the lineup.
The OSight K is the open-emitter sibling with a 6 MOA dot — a large, fast dot suited to close-range defensive use. It ships with an RMR-to-RMSc adapter, so the same optic can move to an RMR-cut slide later. Both use a side-loading battery, so the optic stays zeroed through a battery change.
Meprolight MPO Pro-S — Best Circle-Dot Reticle
The Meprolight MPO Pro-S pairs a circle-dot reticle with the RMSc / J-Point footprint. The ring helps you pick up the optic fast under stress — it is much harder to "lose the dot" in a small window — while the center dot still lets you aim precisely. For a shooter moving from iron sights to a subcompact red dot, this is the easiest reticle to learn, and it runs a CR2032 rather than the smaller cells common in this size class.
Sightmark Minishot A-Spec M3 — Budget Range Optic
The Sightmark Minishot A-Spec M3 is built for the RMS-c footprint with auto-brightness control, an aluminum housing, IP55 water resistance and co-witness with standard pistol sights. IP55 is splash resistance, not immersion — a range and home-defense optic rather than an all-weather duty piece.
Trijicon RMRcc — Best Glass, Different Footprint
The Trijicon RMRcc with a 3.25 MOA dot is purpose-built for slim slides: 7075-T6 housing, IPX7, 1 MOA adjustments, 17mm x 16mm window. It is the cleanest dot in the category and the most durable option here.
The catch is the footprint. The RMRcc uses its own pattern and does not mount on an RMSc cut, so a factory Glock 43X MOS or Glock 48 MOS slide will not take one directly — you need a slide milled for RMRcc or an RMRcc-specific plate. Worth considering if you are already replacing the slide; skip it if you are working with the factory MOS cut.
Battery Life on Small Optics
Subcompact optic housings have less room for a cell, and battery claims in this class vary far more than on full-size optics. Here are the figures the manufacturers actually publish for the optics above:
- Trijicon RMRcc — CR2032, side-loading, up to three years at brightness setting 4
- Viridian RFX42 — up to roughly 28,000 hours, helped by the efficiency of a green LED
- Meprolight MPO Pro-S — CR2032, the same cell used in most full-size optics
- OSight K and SE — side-loading replaceable battery, so the optic stays on the slide and keeps its zero through a change
Where a manufacturer does not publish a figure we have left it out. Treat every published hour count as a ceiling rather than an expectation, and change the battery on a calendar schedule if the gun is carried.
Dot Crispness and Glass Quality
Small optic windows make dot quality more visible. A slightly fuzzy dot in a full-size RMR window can be ignored; the same dot in a 43X-size optic dominates your sight picture. Astigmatism makes this worse, and it is the most common reason a shooter dislikes a red dot they otherwise chose well.
If you know you have astigmatism, a larger dot or a circle-dot reticle usually reads cleaner than a small one — the 6 MOA OSight K, the circle-dot MPO Pro-S and the 2 MOA-plus-32 MOA-circle OSight SE are the practical choices, and a green dot such as the RFX42 helps some shooters. If you train outdoors in direct sun regularly, budget for the Trijicon tier; for mixed and indoor lighting the entry-tier optics hold up fine.
Adapter Plates — What If Your Optic Isn't RMSc?
The RMSc footprint has spread well beyond slim Glocks, so one optic pattern can cover several pistols. Note that these plates adapt other pistols to accept a K/RMSc optic — a factory Glock 43X MOS or Glock 48 MOS already has the RMSc cut and needs no plate.
- Calculated Kinetics Glock MOS to Holosun K / RMSc — puts a K/RMSc optic on a full-size Glock MOS slide, so one optic pattern covers your carry gun and your range gun. Fits Glock MOS models but explicitly excludes the 43X; 9mm MOS slides only. Includes hardware, a Torx bit and thread locker.
- Calculated Kinetics Glock Gen 5 / Gen 6 MOS to K / RMSc — the same idea for Glock's newer Optic Ready System, in 7075 hard-coat anodized aluminum.
- Calculated Kinetics Hellcat OSP to K / RMSc — dual-thickness plate that adapts a Springfield Hellcat OSP cut for a low co-witness fit.
- Trijicon RMSc Adapter Plate for Springfield Hellcat — Trijicon's own plate for the same job.
- Calculated Kinetics CZ P-10 OR / Shadow 2 to K / RMSc — the same adaptation for CZ's optic-ready cuts.
- Viridian RFX44 to S&W Shield RMSc adapter — plate only, and specific to the Viridian RFX44 optic on an S&W Shield RMSc-cut slide.
Plate fitment follows the slide cut, not the model name — two pistols with the same name and different production years can have different cuts. Confirm what your slide is actually milled for before ordering.
Suppressor-Height Sights and Co-Witness
Once the optic is on the slide, your existing irons may no longer line up through the optic window. Suppressor-height sight sets for the Glock 43X and Glock 48 family raise the irons enough to be visible through an RMSc optic. The Sightmark Minishot A-Spec M3 above is specified to co-witness with standard-height pistol sights, so check the spec on whichever optic you choose before buying taller irons you may not need. Selection here is narrower than for the Glock 17 and Glock 19; verify availability at the time of purchase. Our co-witness guide covers the geometry in detail.
What Doesn't Fit on a 43X or 48
Some clarifications, because we field these questions every week:
- RMR Type 2 (full-size RMR) — does not fit. The slide is too narrow for the RMR housing, and the MOS slide is cut RMSc, not RMR.
- Aimpoint ACRO P2 — does not fit. Footprint and slide width are both wrong.
- Holosun 507c — does not fit. The 507c uses the full-size RMR footprint.
- Holosun 407K / 507K — fits. These are K-footprint, which is the same pattern as RMSc.
- Trijicon RMRcc — does not fit a factory MOS cut. Its footprint is its own.
- Holosun EPS Carry — check before ordering. The EPS Carry is close to the K/RMSc family but specific applications may need a dedicated plate.
Optic-Ready vs Aftermarket Slide: Two Paths
Path 1 — Factory MOS Slide, Direct Mount
If you bought a Glock 43X MOS or Glock 48 MOS, the slide already carries the RMSc cut. An RMSc-pattern optic mounts to it directly, with no adapter plate in between. This is the cheapest and lowest-hassle path, and it is why the optics above are grouped by footprint rather than by pistol.
Path 2 — Aftermarket Slide Cut for the Optic You Want
If you have a non-MOS Glock 43 or 43X and want a red dot, you need a slide milled for an optic. RMSc-cut slides for the slim Glock frames turn over quickly and specific finishes move in and out of stock week to week, so rather than name models that may be gone by the time you read this, browse the current Glock slides category and filter for RMSc-cut options. Slides listed as RMSc-cut take the same optics covered here. Our assembled slides are assembled in-house; stripped slides ship as the slide only.
Where to Go From Here
For a carried Glock 43X or Glock 48, the Viridian RFX42 is the pick — enclosed emitter, sized for a slim slide, and the smallest sealed housing in the group. The OSight SE is the value alternative if you want an enclosed emitter and a circle-dot reticle for less, and the Meprolight MPO Pro-S is the easiest reticle to learn coming off iron sights. Browse the pistol optics category for everything we carry on the RMSc / K / J-Point pattern, or read our red dot footprint guide if you are still choosing between footprint families. Laws vary by state; verify local regulations before purchasing.
DISCLAIMER: "GLOCK" is a federally registered trademark of GLOCK, Inc. and is one of many trademarks owned by GLOCK, Inc. and GLOCK Ges.m.b.H. Neither 3CR Tactical nor this site are affiliated in any manner with, or otherwise endorsed by, GLOCK, Inc. or GLOCK Ges.m.b.H. The use of "GLOCK" on this page is merely to advertise the sale of GLOCK pistols, parts, or components. For additional genuine GLOCK, Inc. and GLOCK Ges.m.b.H products and parts visit www.glock.com.