Description
The Holosun 510C Spacer FDE (Holosun item 510C-SPACER-FDE) is a riser plate that lifts the Holosun HS510C reflex sight to lower 1/3 co-witness height on an AR-15 or other flat-top rifle. It is finished in Flat Dark Earth to match FDE builds and the FDE version of the 510C, and it installs between the optic and its integrated quick-detach mount.
Holosun 510C Spacer FDE Overview
Out of the box, the Holosun HS510C sits at absolute co-witness height, meaning the red dot lines up exactly with standard AR-15 iron sights. Many shooters prefer lower 1/3 co-witness, where the iron sights sit in the bottom third of the window. That leaves a cleaner, less cluttered view through the optic while still letting you use the irons if the battery dies. This spacer provides that extra height in a simple, bolt-on part.
What Lower 1/3 Co-Witness Means
With absolute co-witness, the front sight post sits right in the middle of the window. That works, but it can block part of the target. Lower 1/3 raises the optic so the irons appear only in the bottom portion of the window. The result is a more natural, heads-up shooting position for most AR-15 stocks, and a faster, clearer view of the target when you are moving or shooting with both eyes open.
Installation
Remove the 510C from its quick-detach mount, place the spacer between the optic and the mount, and reinstall using the included mounting hardware. Tighten the screws evenly, then reattach the mount to your Picatinny rail and confirm the throw lever locks firmly. Re-zero the optic after installing the spacer, since the change in height moves the point of impact at close range.
Matching an FDE Build
The Flat Dark Earth finish suits rifles with FDE furniture, Cerakote uppers or an FDE 510C. If your optic and rifle are black, a black version of this spacer is also sold separately.
About the Holosun HS510C
The HS510C is an open reflex sight with a large window, a titanium hood, solar backup power and a multi-reticle system that lets you switch between a 2 MOA dot, a 65 MOA circle or both. Its quick-detach mount clamps to any Picatinny rail. Adding this spacer keeps all of those features and simply changes the height of the window relative to the rifle.
Zeroing After Installation
Because the dot sits higher after you add the spacer, confirm your zero at 50 yards and again at 100 yards. Many AR shooters use a 50-yard zero for a flat trajectory out to about 200 yards with 55 grain ammunition. Write down your settings so you can return to them quickly if you ever remove the spacer.
Honest Limitations
This spacer is made for the Holosun HS510C and its mount; it will not fit other optic footprints. Raising the sight line also increases the offset between the dot and the bore, so expect slightly more holdover on very close targets. FDE anodizing can vary slightly in shade from your rifle or optic. Only one verified distributor photo of the FDE version is currently available.
Specifications
- Brand: Holosun
- Model: HS510C Spacer, lower 1/3 co-witness
- Item number: 510C-SPACER-FDE
- UPC: 605930625493
- Fits: Holosun HS510C
- Color: Flat Dark Earth
- Includes: Mounting hardware
Before You Buy
Confirm you own a Holosun HS510C and want lower 1/3 co-witness height. Optic accessories are not firearms, so no FFL transfer is needed and this ships straight to your door.
Who It Is For
The Holosun 510C Spacer FDE is a great fit for AR-15 owners running a 510C who want a cleaner sight picture and a more upright head position with backup iron sights.
Buy the Holosun 510C Spacer FDE at MAG5 Firearms
MAG5 Firearms is a family-owned FFL in Collegeville, Pennsylvania. Order the Holosun 510C Spacer FDE online, or browse our optics section for red dots, mounts and accessories. For factory details, visit Holosun.
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