SIG P365-FUSE and AXG Optic Fit: RMSc or SIG-LOC?
How to identify RMSc versus SIG-LOC on P365-FUSE and P365-AXG variants before buying a red dot or mounting hardware.
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Do not assign one optic cut to every P365-FUSE or P365-AXG by model name. SIG's current documentation shows SIG-LOC entering these lines, including a factory ROMEO-X SIG-LOC FUSE configuration, while P365-family generations and slides vary. Remove the filler plate and use SIG's physical test: raised bosses identify COMPACT/Shield RMSc; flush screw holes identify SIG-LOC. Then buy for the observed cut.
FUSE and AXG are precisely where a family-name fit table becomes risky. SIG is introducing SIG-LOC across current P365 configurations, while older and sibling slides remain in circulation.
Current Evidence
SIG’s current 2026 defense catalog describes the P365-FUSE optic-ready configuration as compatible with SIG-LOC and RMS-C footprint optics and lists a factory-installed ROMEO-X SIG-LOC enclosed configuration. SIG also sells a SIG-LOC 3.7-inch slide that fits P365-AXG and FUSE-size grip modules.
That proves SIG-LOC is present in the ecosystem. It does not prove that every pistol ever labeled FUSE, AXG, or AXG Legion carries that slide.
The Cut, Not the Grip, Controls Fit
P365 modularity makes the distinction especially important. A slide can move across compatible grip-module sizes, so frame markings and grip shape do not identify the optic interface.
Use SIG’s current P365 operator manual:
| Under the filler plate | Cut | Supported starting class |
|---|---|---|
| Raised bosses | COMPACT / Shield RMS-c | RMSc optics; exact K route needs its own proof |
| Flush screw holes | SIG-LOC Compact | Dedicated SIG-LOC optic plus Shield RMS-C optics |
If there is no removable factory filler plate, stop and follow the actual slide maker’s documentation.
Buying Paths
Confirmed COMPACT / RMSc slide
Start with a documented RMSc optic such as the ROMEO-X Compact, ROMEO-X Enclosed Compact, or Shield RMSc. A Holosun K optic is not automatically identical to RMSc; require an exact slide/optic or slide/adapter listing.
Confirmed SIG-LOC slide
The ROMEO-X SIG-LOC Compact is the dedicated bottom-mounted option. SIG says it is exclusive to SIG-LOC-ready P365 slides. The slide can also take Shield RMS-C optics from the top, which preserves a broader optic selection.
Do not use “backward-compatible” to infer Holosun K. SIG specifically names Shield RMS-C; K changes recoil-socket geometry.
FUSE-Specific Conclusion
For a current exact SKU whose SIG documentation says SIG-LOC and RMS-C, both classes have documented routes. For any FUSE already in hand, the physical cut is still the decisive check. For used inventory, older stock, dealer-exclusive configurations, or a swapped slide, inspect rather than assuming.
AXG-Specific Conclusion
“AXG” describes the alloy-grip configuration, not a permanent optic footprint. Current accessories distinguish generations of AXG Legion, and compatible replacement slides can change the interface. Require the exact SKU or under-plate view.
That conservative rule prevents two expensive errors:
- buying the dedicated SIG-LOC optic for an RMSc-only AXG slide; or
- overlooking SIG-LOC because an article assigned all AXG pistols the older RMSc cut.
Confirm the interface in the P365 footprint guide, compare SIG-LOC vs. RMSc, and then open the Fit Checker.
Frequently Asked Questions
What footprint is the P365-FUSE?
SIG's 2026 defense catalog documents the current optic-ready FUSE configuration as compatible with SIG-LOC and RMS-C optics, and lists a factory ROMEO-X SIG-LOC version. Verify the exact commercial SKU and inspect the slide before applying that answer to an earlier or different FUSE.
What footprint is the P365-AXG Legion?
AXG/AXG Legion spans configurations and generations. The model name alone is not enough to distinguish a COMPACT/RMSc slide from SIG-LOC. Use exact SKU documentation or SIG's raised-bosses versus flush-holes inspection.
Can an RMSc optic fit a SIG-LOC FUSE or AXG slide?
Yes when the exact slide is documented as SIG-LOC Compact with Shield RMS-C support. Use the RMSc optic's top-mount hardware, not the dedicated SIG-LOC optic's bottom-mount procedure.
Can the ROMEO-X SIG-LOC fit every FUSE or AXG?
No. SIG describes that optic as exclusive to SIG-LOC-ready P365 slides. A COMPACT/RMSc-only slide cannot accept it.