Glock 43X MOS Red Dot: Which One Actually Fits?
Published on: October 12, 2026
Reading Time: 7 mins
Shopping for a Glock 43X MOS red dot and getting conflicting answers online? You’re not alone.
The right pick depends on your slide’s exact cut, not just which optic has the best reviews. Every Glock 43X MOS takes Shield RMSc-footprint optics with no plate, while Holosun’s popular K-series only mounts directly on Glock’s newer slide cut.
If you’re looking for the best red dot sights for your Glock 43X MOS, this guide covers what fits, how to check your slide, and which optic suits your carry.
Highlights
- Every Glock 43X MOS takes Shield RMSc-footprint optics with no adapter plate.
- Glock’s newer MOS-K cut also lets the Holosun 407K, 507K, and EPS Carry mount directly.
- Older MOS-cut slides still need a plate for those same Holosun optics.
- Glock never renamed the pistol after the update, so two 43X MOS boxes on the shelf can hide different slide cuts.
- Full-size optics like the Trijicon RMR simply won’t fit this slide.
What Red Dot Fits Glock 43X MOS? The Quick Answer
Here’s the short version. If your optic uses the Shield RMSc footprint, it bolts straight onto any Glock 43X MOS.
Holosun’s K-series optics work differently: they need a plate on the original cut but mount directly on the newer MOS-K cut.
Full-size, RMR-footprint optics don’t fit this slide at all, with or without a plate. They’re simply too narrow.
| Optic type | Older MOS cut | Newer MOS-K cut |
|---|---|---|
| Shield RMSc-footprint optics | Direct mount | Direct mount |
| Holosun K-series (407K, 507K, EPS Carry) | Needs adapter plate | Direct mount |
| RMR-footprint optics (Trijicon RMR, Holosun 507C) | Doesn’t fit | Doesn’t fit |
One more thing: the Glock 48 MOS shares this exact slide cut, so everything here applies to it, too.
MOS vs. MOS-K: Which Slide Cut Do You Have?
Not every Glock 43X MOS is built the same.
The “MOS” on this pistol isn’t the system found on a Glock 19 or 17 MOS, which use interchangeable plates. Your slimline 43X MOS has one fixed cut instead.
At some point, Glock started shipping Slimline MOS pistols with a second, revised cut. The original cut accepts only the Shield RMSc footprint, while the newer MOS-K cut also accepts Holosun’s K-series footprint without a plate.
How to Tell Which Cut You Own
Checking your slide takes two steps, both straight from Glock’s own instructions:
- Look at the item number sticker on your pistol case. Glock’s page states the standard cut ends in “MOS,” while the newer cut includes “MOSK” near the end.
- Pop off the cover plate and look inside the cut. Four raised posts mean the original cut, and two posts mean MOS-K.
No box anymore? The post count is your best bet, and it’s the same check a gunsmith would run.
Outside of Glock’s own page, sources don’t always agree on exactly where those two remaining posts sit. Skip the guesswork and count for yourself.
What If Your 43X Isn’t a MOS?
A standard, non-MOS Glock 43X has no optic cut, so there’s nothing to bolt a red dot onto.
Your options are slide milling, an aftermarket slide with a cut, or a dovetail-mount plate. Milling is permanent, so talk to a licensed gunsmith first.
Red Dots That Mount Directly to the Glock 43X MOS
For the simplest setup, stick with a true Shield RMSc-footprint optic. These bolt straight onto both slide cuts, with no extra parts needed.
A few solid direct-mount options include:
- Shield RMSc or SMSc—the original optic the cut was designed around.
- SIG Romeo Zero—an affordable, polymer-bodied entry point.
- SIG Romeo-X Compact—a sturdier aluminum step up from the Romeo Zero.
- Swampfox Sentinel II—an aluminum housing with a larger viewing window.
- Vortex Defender-CCW—built specifically for compact carry pistols like this one.
Each trades some battery life and reticle variety for plug-and-play simplicity, which is a fair trade for many carry setups.
Always double-check an optic’s footprint on the manufacturer’s own product page before buying, since footprints can change between model years.
Holosun 407K, 507K, and EPS Carry on the Glock 43X MOS
Holosun’s K-series optics are some of the most talked-about red dots for this pistol, and whether they need a plate depends entirely on your slide cut.
Direct Mount on the MOS-K Cut
If your slide has the newer MOS-K cut, skip the plate. The 407K, 507K, and EPS Carry all bolt straight to the slide, giving you a lower mounting height and one less part in the way.
Adapter Plate on the Older Cut
On the original slide cut, these same optics need a plate, since the K-series footprint doesn’t match the older cut’s post layout.
A plate adds height above the slide, and how much depends on the plate. Check the manufacturer’s listed dimensions before buying, rather than guessing.
Some listings bundle an RMSc-to-K adapter plate with the EPS Carry, but that’s not guaranteed on every version. Confirm what’s included at checkout, and test-fit any bundled plate before mounting anything permanently.
407K vs. 507K vs. EPS Carry
The three optics share a footprint, but each serves a different need:
- 407K—a single 6 MOA dot, nothing fancy, and budget-friendly.
- 507K—adds a multi-reticle system: dot only, circle only, or both together.
- EPS Carry—the enclosed-emitter option, sealed against lint and moisture.
Choosing the Best Red Dot for Glock 43X MOS
Which one should you buy? It comes down to how you use the gun day to day.
A quick way to narrow it down:
- Want zero extra parts? Pick a direct-mount RMSc optic.
- Have the MOS-K cut and want more features? Go with a Holosun 507K.
- Carry inside the waistband daily? An enclosed-emitter optic keeps lint and pocket debris out.
- Working with a tight budget? The SIG Romeo Zero or Holosun 407K both cover the basics for less.
Dot size matters, too. A smaller 2 MOA dot offers more precision at distance, while a larger 6 MOA dot is faster to find up close, which most carry situations call for.
Our pick for most 43X MOS owners is a Holosun 507K, direct-mounted if your slide allows it. You get a multi-reticle system, long battery life, and a side-loading battery tray, all in one compact package.
Mounting Tips: Screws, Torque, and Co-Witness
A clean install protects your zero long-term, and it starts with the screws.
Screws and Threadlocker
Never reuse the screws that held your factory cover plate. Glock says those are made for the plate, not the optic.
Use the screws that came with your optic instead, short enough not to poke through the bottom of the mount. A clean install follows this order:
- Degrease the slide and screw threads with rubbing alcohol.
- Add a small drop of blue threadlocker to each screw.
- Torque to the exact spec listed in your optic’s manual.
Iron Sight Co-Witness
Whether your factory sights show up through the window depends on your optic, plate, and sight height. No single answer covers every setup, so test it before you carry it that way.
Holster Fit
Once you mount your optic, your old holster won’t work. You’ll need one cut for your exact optic, not just the pistol.
Common Mistakes to Avoid
A few small errors cause most fitment headaches on this pistol:
- Buying a plate before checking your slide cut.
- Grabbing a plate made for a full-size Glock 19 or 17 MOS. It won’t fit here.
- Assuming “K footprint” and “RMSc” mean the same thing. They’re close cousins, not identical twins.
- Mounting an RMR-footprint optic on this slide. It’s simply too wide.
- Skipping threadlocker, or grabbing the wrong color by mistake.
FAQ
Does the Holosun 507K fit a Glock 43X MOS?
Yes. It mounts directly on the newer MOS-K cut. On the older cut, you’ll need an adapter plate.
Do I need an adapter plate for a red dot on a Glock 43X MOS?
Only for K-series Holosun optics on the original slide cut. RMSc-footprint optics never need one.
What red dot fits a Glock 43X MOS without a plate?
Any Shield RMSc-footprint optic fits both cuts. Holosun K-series optics skip the plate only on the newer MOS-K cut.
Does the Holosun EPS Carry direct mount to a Glock 43X MOS?
Yes, but only on the MOS-K cut. On the older cut, it needs an RMSc-to-K adapter plate, which is bundled or available separately.
Can I put a red dot on a Glock 43X that isn’t a MOS?
Not without extra work. You’d need slide milling, a pre-cut aftermarket slide, or a dovetail-mount plate.
Will the same optic fit a Glock 48 MOS?
Yes. The 48 MOS uses the identical slide cut, just on a longer pistol.
How do I know if I have the MOS-K cut?
Check your case’s item number for “MOSK,” per Glock’s own labeling, or pull the cover plate and count the posts. Two posts mean MOS-K.
Conclusion
Finding the right Glock 43X MOS red dot comes down to one question: which slide cut do you have? Shield RMSc-footprint optics fit either way, while Holosun’s K-series needs a plate on the older cut and mounts directly on the newer one.
Ready to gear up? Gold Trigger carries red dot sights built for the Glock 43X MOS and every other carry setup. Browse our selection or call us at 713-485-5773, and we’ll help you find the right fit.
Disclaimer: This article is for informational and educational purposes only and isn’t a substitute for professional or legal advice. Slide cuts, specifications, pricing, and availability, including Glock’s MOS and MOS-K optic cuts, are subject to change and should be verified with Glock, the optic manufacturer, or the retailer before purchase. Only lawful owners should install, mount, zero, and use firearm optics in full compliance with applicable laws. We recommend having a qualified gunsmith mount and zero your optic, and only a licensed professional should do slide milling. Gold Trigger doesn’t condone illegal activity and isn’t responsible for any misuse of products or information here. Consult a licensed attorney or local law enforcement if you’re unsure about legality in your jurisdiction.
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