SIG P320 X-series optic footprint and plates

Identifying the five plates, and the cut underneath them

Two different questions get asked here and they have different answers. The first is what your slide is cut for. The second, once a plate kit is in your hand, is which plate goes with which optic.

The pocket. Lift the plate out of the rear of the slide and look at the floor of the recess. On this system it is flat and featureless apart from the threaded holes the plate screws into: no posts, no bosses, nothing for an optic body to locate on. Those locating features live on the top face of the plate instead. A slide with bosses standing proud inside the recess is cut for an optic pattern directly and is not on this system. Every SIG in this dataset resolves on one rule: if it is a P320 it takes a plate, and if it is a P365, a P322 or a SIG 1911 it does not. The model-by-model working of that split, all 29 SIG pistols, belongs to the SIG P320 optic plate guide and is not repeated here.

The plates. This is the part no compatibility widget covers. The 5 plates recorded for this system present 5 different patterns, and what separates them is visible on the plate’s top face before anything is torqued down:

• The RMR plate. 2 screw holes with 2 recoil lug sockets set forward of them. That two-socket layout is unique among the five, so this plate identifies itself by eye (opticsplanet.com).
• The RMSc plate. 2 screw holes with 4 bosses at the corners, in the shorter optic class, roughly 40mm of sight body sitting on it (badassoptic.com).
• The DeltaPoint Pro plate. The same 2 screws and 4 corner sockets, in the longer class, roughly 46mm (optics-trade.eu).
• The Docter plate. Again 2 screws and 4 corner sockets (opticsplanet.com). The tell is the optic rather than the plate: this is the path that carries the Burris FastFire 3 and 4, the Vortex Venom and Viper, the Crimson Trace CTS-1250 and the Primary Arms SLx RS-10.
• The C-More STS plate. 2 long screws into a flat base with no recoil sockets at all, which makes it the other plate that gives itself away (survivalstoic.com).

Read that list carefully and the honest limit arrives with the method. Socket count separates the RMR and C-More STS plates from the other three and stops there. The RMSc, DeltaPoint Pro and Docter patterns all record 2 screws and 4 corner sockets in this dataset, which publishes no screw spacing and no socket diameter for any of them. Identify those two plates by eye; identify the other three by matching the pattern named on your optic’s own spec page, never by counting holes.

Why this site records no direct-fit optic on a P320

The tables on this page say 0 optics mount on the P320 cut itself, and P320 product listings say the opposite in plain words. Both are right, and the reason is worth understanding before you buy anything.

The X-series slide’s native interface is SIG’s own PRO cut. SIG describes the P320 XCarry Legion slide as “compatible with the ROMEO1PRO, ROMEO2, PRO footprint, and RMR” (sigsauer.com); the P320 SXG Reserve spec line reads “Optic Ready (PRO Footprint)” (scheels.com) and the P320 Full Size reads “optic ready slide w/PRO optic footprint” (scheels.com). An AXG Pro listing goes further: “The optic-ready Pro-cut slide is fitted with XRay3 day/night sights and compatible with Romeo1PRO, ROMEO2 and Deltapoint PRO optics for a direct-to-slide fit without the need for adaptor plates” (sportsmansoutdoorsuperstore.com). The plate makers use the same vocabulary, listing their P320 plates as an “R1P/DPP Cut to Trijicon RMR” (chpws.com).

This dataset does not carry a SIG PRO footprint record. The ROMEO1PRO itself is in the catalogue, sourced to opticsforce.com, with no pattern attached, so it produces no optic page and sits in none of the counts on this page. The practical consequences, stated plainly:

• Every optic this site records for a P320 is recorded through a plate. That is the conservative reading, not a claim that a plate is physically unavoidable on every configuration.
• If your slide is the Pro cut and your optic is a ROMEO1PRO, a ROMEO2 or a DeltaPoint Pro, check the pistol’s own paperwork before buying a plate. The listings above describe that combination mounting without one.
• The 46mm class explains the overlap. This dataset’s DeltaPoint Pro record names the SIG Romeo1Pro among the sights sharing that pattern (optics-trade.eu), which is why SIG’s “PRO footprint” and the DeltaPoint Pro plate path keep pointing at the same optics.

A PRO footprint record, and a SIG plate kit page to replace the aftermarket listing this system is seeded from, are the two things that would settle this. Neither is in the dataset today and the page says so rather than papering over it.

Pattern and dimensions

What this dataset publishes for the SIG P320 X-series system:

Property	Value	Source
Kind	Plate system, not a footprint	dataset
Mounting style	Proprietary plate	dataset
Plate retention screws	Not recorded	dataset
Bosses in the slide pocket	None, the plate carries them	dataset
Pistols on the system	16 of 196	dataset
Plate paths recorded	5, presenting RMR, RMSc, DeltaPoint Pro, Docter and C-More STS	outerimpact.com
Optics that mount with no plate	0	dataset

The summary chips above this section read “Screw count: 0” and no recoil lug count at all. On a plate system 0 means not recorded, not “no screws”: the plate is retained by fasteners and this record does not carry their count, thread or spacing. Pocket dimensions, plate part numbers and factory kit contents are unpublished here too. The rule on this site is to print a null rather than a guess, so none of those figures appears above.

One sourcing limit shapes the whole page. All 5 plate paths trace to a single listing for an aftermarket modular adapter that fits these slides, not to a SIG technical document (outerimpact.com). The pistols are better sourced, several of them to sigsauer.com itself. On the optic side of the page, the number to know is that 41 of the 100 optic pages in this dataset carry a verified provenance flag today, 39 of them on the 85 a P320 reaches. The rest is sourced research rather than a checked physical sample.

Look-alikes that will not interchange

The system against a footprint. There is no SIG P320 footprint to shop for, and searching for one is how people buy the wrong part. The pocket takes a plate, the plate carries a pattern, the pattern is what the optic is built to.

The RMSc plate against the DeltaPoint Pro plate. The most expensive mix-up available on this pistol, because the two share a hole pattern and differ only in body length, roughly 40mm against roughly 46mm (opticsplanet.com). An optic from the wrong class will not sit down on the plate no matter how convincing the four sockets look. Read the pattern off the optic’s page, never off the holes.

A P320 plate against another system’s plate. Every factory plate system works the same way and none of their plates swap. Glock MOS, Canik METE, S&W M&P CORE, FN 509, Walther PDP 2.0, CZ P-10 OR and Taurus TORO are each cut for their own pocket. Canik presents the identical five patterns this system does and its plates still do not fit a P320.

The P320 against the P365. Same maker, opposite mounting worlds. The P365 family is cut for RMSc in the slide and mounts without a plate; the P320 is not. An X in the model name settles nothing, on either gun.

A Holosun K optic against the RMSc plate. Holosun K is RMSc with the rear pair of lugs deleted, tracked here as its own pattern for that reason (opticsplanet.com). Of the 15 plate systems in this dataset exactly 1 presents K, and it is not this one.

A clamp-on optic against any of this. If the sight locks onto a groove with a cross bolt instead of bolting down through its own body, it is an ACRO interface optic (optics-trade.eu), and no P320 plate recorded here presents it. The Holosun 509T uses a different clamp again and is not cross-compatible with ACRO either.

How a plate gets you to a footprint

In words: the slide is machined for a pocket. A plate drops into that pocket and its top face carries a real footprint. Fit the plate that presents RMR and the pistol behaves, for optic-shopping purposes, like an RMR pistol. Fit the RMSc plate instead and the same pistol behaves like an RMSc pistol. Nothing about the slide changed; the interface on top of it did.

The 5 paths recorded here, and what each one opens:

• The RMR plate: 33 RMR optics from 7 brands, the longest single list reachable on this pistol and the pattern with the deepest mount and holster ecosystem behind it. Holosun alone accounts for 16 of the 33. The source listing carries one caveat worth repeating: “Trijicon RMR/SRO, some weapons may experience ejection issues using the SRO” (outerimpact.com).
• The RMSc plate: 30 RMSc optics from 12 brands, the widest brand spread of the five and the most compact bodies. The same listing notes that the Shield RMS “requires a purchase of these screws”, so budget for fasteners on this path specifically.
• The DeltaPoint Pro plate: 15 DPP optics from 5 brands, in the longer body class, and the path that overlaps SIG’s own PRO cut.
• The Docter plate: 6 Docter optics from 4 brands. A short list carrying several of the most widely owned budget open sights, so it is the whole decision if one of them is already on the bench.
• The C-More STS plate: 1 C-More STS optic and nothing else in this dataset. Of the 15 plate systems here, 4 present that pattern at all.

Those five groups do not overlap. No optic page appears on two of them, so the paths sum exactly to 85 of the 100 optic pages, from 15 of the 16 optic brands this dataset holds, across 103 SKUs. Whichever plate goes on the gun therefore removes at least 52 of those 85 from consideration before you have looked at a reticle.

Where this system sits among the others: 10 of the 15 plate systems present Docter and 4 present C-More STS, so carrying both is what lifts the P320 above the four-path systems. It pays for that with the pattern it does not carry.

What a P320 cannot mount

85 of 100 leaves 15 optic pages out of reach, in four groups. This is the part a compatibility chart will not tell you before you buy.

• The 5 ACRO pattern optics. There is no ACRO plate in this system. 9 of the 15 plate systems here have one, which makes the P320 the largest plate system in this dataset with no ACRO path. Every ACRO pattern optic recorded here is an enclosed emitter design, and the one optic brand a P320 cannot reach at all, Aimpoint, is missing for this one reason. Steiner is reachable, but only for the MPS-C and only through the RMSc plate.
• The 5 Holosun K pattern optics. No plate here presents K, and only 1 plate system in the whole dataset does.
• 2 optics built for another maker’s pocket, which take the Glock MOS and Walther PDP 2.0 cuts and nothing else.
• 3 optics that currently fit no pistol at all in this dataset, so their absence here says nothing about the P320.

The gap is narrower than it sounds for anyone who wants a sealed emitter rather than an Aimpoint specifically. 16 of the 27 enclosed optics in this dataset are reachable on a P320, spread across three of the five plates: 8 on the RMSc path, 5 on the DeltaPoint Pro path and 3 on the RMR path. The Docter and C-More STS paths carry no enclosed optic at all.

How to choose a P320 plate and optic

No prices on this page and no rankings the data cannot support. What the data does support:

• Choose the optic first, then buy the plate it needs. The plate is a consequence, not a preference. Going the other way is how people end up with a mount that presents a pattern nothing on their shortlist uses.
• Check for the PRO cut before you buy a plate at all. If the optic you want is a ROMEO1PRO, a ROMEO2 or a DeltaPoint Pro, the listings quoted above describe it mounting to a Pro-cut slide directly. This dataset cannot confirm that for your model, and it is worth five minutes with the pistol’s paperwork.
• Widest choice: the RMR or the RMSc plate. 33 pages against 30. RMR is the longer list; RMSc is the wider brand spread at 11 brands and the most widely cut pattern in this dataset, with 80 pistols milled for it directly, so it is the safer pattern to standardise on across a collection.
• If you also own a P365, take the RMSc plate. It is the only pattern a P320 plate and a direct-cut SIG slide both accept, so one optic model covers both guns.
• Enclosed emitter: start on the RMSc plate, which carries 7 of the 15 enclosed options reachable here, and rule the Docter and C-More STS paths out first because they carry none.
• If the requirement is an Aimpoint ACRO or a Steiner MPS, this is the wrong pistol and no plate in this dataset changes that.
• Budget for the plate and its screws every time. Adding a plate raises the optic by the plate’s thickness, so the screws that came in the optic box were sized for a slide without one. The RMS path carries an explicit screw warning on the source listing.

Nothing on this page is verified against a physical sample. Every fit claim is sourced research, a manufacturer or retailer page recorded against the record it supports, and no SIG plate drawing is yet among those sources. Confirm against your own pistol before you spend money.

Where to go next

• The full chart: all 24 optic footprints and plate systems.
• The long form article this hub owns, including the model-by-model split of every SIG pistol here: SIG P320 optic plate guide.
• Why a plate is needed at all: do you need an adapter plate?
• The two patterns most buyers here choose between: RMR footprint guide and RMSc footprint guide, compared in RMR vs RMSc.
• The path that overlaps SIG’s own PRO cut: DeltaPoint Pro footprint guide.
• The other half of SIG’s lineup, where the slide is cut and no plate is used: SIG P365 red dot compatibility.
• Pistols on this system: P320 XCompact, P320 M17, P320 M18, P320 XCarry Legion, P320-XTEN.
• SIGs that are cut instead of plated: P365X, P365 Optic Ready, 1911-XCarry.
• The same problem on other pistols: Glock MOS, Canik METE, S&W M&P CORE, Springfield XD OSP.