Co-witness on a pistol works differently than on an AR-15, and most of the bad advice online comes from people applying AR-15 sight geometry to a Glock. On a pistol the optic is only a few millimeters above the slide, the irons are short, and there's no riser to push the optic up to a "lower 1/3" position the way an AR-15 carry-handle setup does. This guide covers absolute vs lower 1/3 co-witness as it actually applies to pistols, picks suppressor-height sight sets and optic-complement front sights, and points at the Nordic Components plates that bundle backup sights into the optic mount.
What Co-Witness Means on a Pistol
Co-witness means you can see your iron sights through the optic window when the pistol is presented. If the optic fails — battery dies, glass cracks, dot disappears for any reason — the irons are already in the right position to take the shot without a transition step. On an AR-15, the optic sits on a riser well above the bore, so co-witness math involves the height-over-bore stack of the riser plus the optic. On a pistol, the optic sits directly on the slide, and the irons have to be tall enough to project up through the optic window.
Two configurations get used:
Absolute Co-Witness
The iron sights sit at the same height as the optic window center. When you present the pistol, the dot and the front sight overlay each other in the same vertical plane. Faster to pick up if the optic dies — your front sight is already where the dot was — but the front sight blocks part of the lower half of the optic window during normal use.
Lower 1/3 Co-Witness
The iron sights sit lower in the optic window — front sight visible in the bottom third of the glass when the pistol is presented. The dot lives in the upper two-thirds, undisturbed by the irons. Slightly slower to transition to irons if the optic fails (you have to drop your sight picture slightly), but the optic view stays clean during normal use.
On a pistol the difference between absolute and lower 1/3 is small — maybe a millimeter or two of front sight height. Pick lower 1/3 if you mostly run the optic and want the cleanest dot view; pick absolute if you want the fastest transition to irons.
Why Standard Glock Irons Don't Co-Witness
Factory Glock iron sights are sized for the stock slide profile, which sits below most red dot windows. When you mount any optic — even a low-profile RMR — the standard front sight is too short to project through the optic glass. You see the optic dot but not the front sight underneath it. If the optic dies, you have no backup sight picture.
Two solutions:
- Suppressor-height sights — taller front and rear sights that project up through the optic window
- Optic-complement sights — front sight only, raised to the height the optic window needs, used in combination with the optic for fast aiming and as a backup if the dot fails
Suppressor-Height Sight Sets
Suppressor-height sights were originally designed to clear suppressor cans mounted forward of the muzzle — the irons had to be tall enough to see over the can. The same height range happens to work well for co-witnessing through optic windows, which is why "suppressor-height" became the catch-all term for tall iron sights on pistols.
Typical heights:
- Standard Glock front sight: ~0.165" from slide top
- Suppressor-height Glock front sight: ~0.250" to ~0.315" from slide top
The specific height needed depends on the optic. RMR and RMSc-pattern optics tend to need ~0.250" front sights. ACRO and EPS sit higher on the slide (and higher again if an MOS adapter plate is involved), needing front sights closer to 0.315".
The XL Optic Complement 3-Dot Tritium/White Outline Sight Set uses a 0.315" front and 0.394" rear sight specifically sized for the taller optic stack-ups on MOS plates and enclosed-emitter housings. Tritium front and rear inserts work in low light when the optic is off or failed.
Hi-Viz Co-Witness Front Sights
If you want a high-visibility front sight specifically for co-witness use, the Hi-Viz fiber-optic sight family makes optic-complement variants. The Hi-Viz Co-Witness Fiber Optic Sight Set for Glock 9mm/.40 MOS is purpose-built for MOS pistols — the front sight is sized to project through standard MOS optic windows and the fiber optic insert is bright enough to pick up immediately as a backup if the dot dies.
Inventory note: the Hi-Viz Co-Witness set has been at low stock — verify availability at the time of purchase.
Optic Plates That Bundle Backup Sights
Nordic Components makes a series of optic plates for Glock MOS that include backup iron sights or tritium night sights integrated into the plate. This is the cleanest way to add co-witness backup if you're already buying an adapter plate to run a non-RMR optic on a Glock MOS slide.
Options in stock:
- Nordic Components Optic Plate + Night Sights for Trijicon RMR / Holosun 507c — Glock MOS
- Nordic Components Optic Plate + Backup Sights for Aimpoint ACRO — Glock MOS
- Nordic Components Optic Plate + Backup Sights for Holosun EPS — Glock MOS
- Nordic Components Optic Plate + Backup Sights for Holosun 509T — Glock MOS
- Nordic Components Optic Plate + Night Sights for Holosun 509T — Glock MOS
"Backup Sights" (BS) variants include polymer backup sights integrated into the plate; "Night Sights" (NS) variants include tritium night sights. Pick based on how you carry — duty rigs benefit from tritium for low-light backup, range pistols can save the cost with polymer backups.
Co-Witness Through an Optic Window: Geometry by Optic
Different optics need different sight heights to co-witness because each optic places the dot at a different height above the slide. A rough guide:
| Optic | Footprint | Front Sight Height Range |
|---|---|---|
| Trijicon RMR Type 2 | RMR | ~0.250" |
| Trijicon SRO | RMR | ~0.260" |
| Trijicon RMR HD | RMR | ~0.260" |
| Holosun 507c / 508T | RMR | ~0.250" |
| Aimpoint ACRO P2 | ACRO | ~0.315" (more with MOS plate stack) |
| Holosun EPS Carry | EPS/K | ~0.290" |
| Holosun 509T | 509T | ~0.315" |
| Leupold DeltaPoint Pro | DPP | ~0.250" |
| Sig Romeo-RS Pro | Romeo-RS Pro | ~0.270" |
These are approximate. The cleanest way to confirm exact height: measure the bottom of the optic window above the slide top with a caliper, then add the iron sight blade height you want to see in the window.
Pairing the Right Sight Set to the Right Optic
RMR / SRO / RMR HD (Open RMR Footprint)
0.250" front, 0.394" rear works for most setups. The XL Optic Complement Tritium 3-Dot set uses a slightly taller 0.315" front which still co-witnesses cleanly on RMR-pattern optics — slightly absolute leaning, fast to find on transition. The Nordic Components RMR / 507c plate with night sights integrates the irons into the plate so you don't have to source them separately.
ACRO P2 (Closed ACRO Footprint, On MOS Plate)
0.315" front, 0.394" rear is the typical pairing for ACRO on Glock MOS. The plate stack pushes the ACRO higher than an RMR, so taller front sights are needed. The Nordic Components ACRO plate with backup sights bundles the right-height backup sights into the plate itself.
Holosun EPS / 509T (Enclosed)
0.290"–0.315" front, 0.394" rear. The Nordic Components EPS and 509T plates with integrated backup or night sights cover this pairing in one package.
Glock 43X / 48 MOS (RMSc Optics)
The 43X / 48 use shorter iron sight blade dimensions than full-size Glocks, and the optic window on RMSc-pattern optics sits low on the slide. Sight set selection for 43X / 48 specifically is narrower — verify in-stock at the time of purchase. Most current options come from Truglo, Trijicon HD, and AmeriGlo product lines sized for the 43X / 48 dovetails.
What Not to Try
Three setups that don't work the way shooters expect:
- Standard Glock irons with any red dot — the front sight is too short to project through the optic window. No co-witness, no backup if the dot fails.
- AR-15 lower 1/3 risers on a pistol — this combination doesn't physically exist; pistol red dots don't use risers
- Suppressor-height irons under a low-mounted optic without an adapter plate — tall irons under a low optic can make the rear sight block the optic window from underneath. Verify the front and rear sight heights match the optic window's window-bottom-above-slide measurement.
Where to Go From Here
If you're picking the optic first, work backward through the series: footprint guide, then dot size, then open vs enclosed, then come back here for the co-witness math. If you already own the optic and just need the right iron sights or plate, browse the Glock pistol optics category for Nordic Components plates with integrated sights, or the main pistol optics category for standalone sight sets. The cleanest single-package solution for most Glock MOS shooters: a Nordic Components plate with integrated backup or night sights, sized for the optic footprint you're running.
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