SIG P320 Optic Plate: 5 Plates, 85 Red Dots That Fit

Every one of the 16 SIG P320 models in this dataset mounts a red dot through a removable plate, and not one of them is milled for an optic footprint directly. Those 16 pistols reach 85 of the 100 optic pages here, split across five plates that present the RMR, RMSc, DeltaPoint Pro, Docter and C-More STS patterns. So the first question about mounting a dot on a P320 is never which optic. It is which of the five patterns you are committing to, because the plate is what makes the choice and the plate is bought separately from both parts.

That framing matters more on this pistol than on most, because SIG is the largest pistol brand in this dataset at 29 optic-ready models, ahead of Smith and Wesson at 21 and Glock at 18, and those 29 models run across three different mounting standards at once. Worse, the model name is a poor guide to which one you have. There are SIG pistols with an X in the name that use no plate at all, and SIG pistols with no X in the name that are squarely inside the X-series plate system. Getting that wrong costs you a plate you did not need or an optic that will not sit on the gun.

Every number below is recomputed from the published dataset bundle for this article. The bundle holds 196 optic-ready pistols, 100 optic pages covering 135 individual SKUs, and 24 footprint and plate-system hubs.

The five plates, and what each one reaches

The SIG P320 X-series plate system hub records five plate paths. Each plate presents exactly one footprint, and that footprint decides which optics will bolt on.

Plate presents	Optics reachable	Optic brands	Enclosed emitter
RMR	33	7	3
RMSc	30	12	8
DeltaPoint Pro	15	5	5
Docter	6	4	0
C-More STS	1	1	0

Three things in that table are worth more than the headline number.

First, the five counts sum to 85 exactly, which means no optic in this dataset appears on two of the five plates. There is no hedging option, no optic that lets you defer the decision, no plate that covers a second pattern as a bonus. Whichever plate goes on the gun eliminates 52 or more of the 85 candidates before you have looked at a single reticle or battery spec. On a pistol where the plate is the whole mounting story, that is the most consequential thing to understand about it.

Second, the plate with the most optics behind it is not the plate with the most brands behind it. The RMR plate reaches 33 optics but only 7 brands, because Holosun alone accounts for 16 of those 33 and Swampfox another 5. The RMSc plate reaches fewer optics, 30, but spreads them over 12 brands, including all 7 of the Shield Sights products here and 5 of SIG’s own. If your shortlist is built around a specific maker rather than a specific model, the brand column is the one to read.

Third, the Docter plate looks marginal at 6 optics and is not. It is the only one of the five paths that carries the Vortex Venom and Viper, the Burris FastFire 3 and FastFire 4, the Crimson Trace CTS-1250 and the Primary Arms SLx RS-10, and those six are among the most widely owned budget dots in circulation. If you already own one of them, the Docter plate is the entire decision and the other four rows are noise. This is also the path that separates the P320 from the Glock MOS, which is covered further down.

The fifth path is the narrowest in the dataset. The C-More STS plate reaches exactly one optic, the Primary Arms GLx RS-15, and no other plate in this system presents that pattern. It is on the same aftermarket listing the other four plates come from, and it is worth knowing about for one reason only: if a C-More STS pattern dot is already on the bench, the P320 is one of four plate systems in this dataset that can take it at all.

Fifteen of the dataset’s 16 optic brands are reachable on a P320. The one that is not is Aimpoint, and the missing ACRO plate is the reason.

SIG runs three mounting standards across 29 pistols

This is the section no single hub page can carry, because the answer spans three of them. Here is every SIG pistol in the dataset, grouped by how it mounts.

Mounting standard	SIG models	Optics that fit	How they mount
P320 X-series plate system	16	85	all through a plate
RMSc plus Holosun K, cut in the slide	10	35	all direct, no plate
RMSc only, cut in the slide	3	30	all direct, no plate

The 16 on the plate system are the P320 AXG Legion, AXG Pro, Compact, Full Size, M17, M18, Spectre Comp, SXG Reserve, X-Five Legion, X-Five SXG, XCarry Legion, XCarry Spectre, XCompact, XCompact Spectre, XFull and P320-XTEN.

Read that list again and notice what is in it. The P320 M17 and the P320 M18 have no X anywhere in the name. Neither do the P320 Compact or the P320 Full Size. All four are on the X-series plate system regardless, because the plate system is named after the line it debuted on, not after the models that use it. “X-series plate system” is a pattern name, the same way “Glock MOS” is, and pattern names outlive the products they were named for.

Now notice what is not in it. The SIG 1911-XCarry and 1911-XFull both carry an X in the model name and neither one uses a plate: both are cut for the RMSc footprint directly and take 30 optics with no plate in the stack. The P365X, P365XL, P365-XMACRO and P365 X-Macro TacOps have an X too, and all of them are direct-cut as well. The X tells you nothing about mounting on a SIG. Only the model family does.

The practical rule that falls out of this: if it is a P320, it uses a plate. If it is a P365, a P322 or a SIG 1911, it does not. That single sentence resolves every SIG pistol in this dataset, and it is worth more than any amount of squinting at product photos.

Telling a plate pocket from a footprint on the gun

If the model name on the slide has worn off, or you are looking at a used pistol on a table and cannot look anything up, the cut itself tells you. The difference is visible without tools.

A plate pocket, which is what every P320 here has, is a rectangular milled recess with the removable plate sitting in it, retained by its own screws. Take the plate off and the floor of the pocket is flat and featureless apart from the threaded holes the plate screws into. There are no locating bosses or posts standing up from it, because the bosses live on the top face of the plate, not on the slide. If you are looking at a P320 that came from the factory with no optic, the pocket will usually be filled by a blank cover plate rather than a functional optic plate, and that cover plate is not a mounting plate: it presents no footprint at all and has to be swapped for a real one.

A milled footprint, which is what a P365 or a SIG 1911-XCarry has, has the recoil bosses or lugs machined into the slide itself. Those bosses are the tell, and counting them separates the common patterns. Working from the footprint records in this dataset:

Pattern	Screws	Recoil bosses or lugs	Mounting style
RMSc	2	4	screws pass through the optic
DeltaPoint Pro	2	4	screws pass through the optic
Docter	2	4	screws pass through the optic
RMR	2	2	screws pass through the optic
Holosun K	2	2	screws pass through the optic
ACRO	1	1	dovetail clamp

So on a direct-cut SIG slide, four bosses at the corners of the recess points to the RMSc family, which is what every direct-cut SIG in this dataset uses. Two bosses forward of the screw holes would point to RMR or Holosun K, and no SIG slide here is cut that way. The ACRO row is the outlier in the table and in the article: it is not a screw-through footprint at all but a clamp that grips a rail, which is why it behaves so differently from the rest.

What this dataset does not publish for any of these patterns is screw thread size, screw centre spacing or boss diameter. Those numbers are not recorded here, and rather than guess at them this is stated plainly: if you need to machine something to a tolerance, go to the optic maker’s own drawing, not to this page. Screw length in particular is worth its own warning. Adding a plate raises the optic by the plate’s thickness, and the screws that came in the optic box were sized for a direct-cut slide. Plate makers ship the correct length with the plate for exactly this reason, and the screws in the optic box should be set aside, not reused.

SIG P320 against Glock MOS: 85 versus 83, and different 83

These two plate systems are the closest match in the dataset and the comparison is a genuinely useful one, because a buyer choosing between platforms often assumes one of them opens more doors. On the raw numbers, it barely does.

	P320 X-series	Glock MOS
Pistols in this dataset	16	16
Plate paths	5	4
Optics reachable	85	83
Patterns presented	RMR, RMSc, DPP, Docter, C-More STS	RMR, RMSc, DPP, ACRO

Sixteen pistols each, five plates against four, two optics apart. But the two catalogues are not the same catalogue with two extra items. Three of the paths match, the fourth is a straight substitution and the fifth exists on the P320 only, so each platform reaches a handful the other cannot.

Reachable on a P320 and not on a Glock MOS, the whole Docter path: the Burris FastFire 3, Burris FastFire 4, Crimson Trace CTS-1250, Primary Arms SLx RS-10, Vortex Venom and Vortex Viper, plus the whole C-More STS path, which is the Primary Arms GLx RS-15. Seven optics, all open emitter.

Reachable on a Glock MOS and not on a P320, the whole ACRO path: the Aimpoint ACRO C-2, ACRO P-1, ACRO P-2, Burris FastFire E and Steiner MPS. Five optics, and here is the part that matters: all five are enclosed emitter.

That is the real difference between the two platforms in this dataset, and it is not a difference of size. It is that the P320 trades access to five enclosed ACRO pattern sights for access to six popular open budget sights and one competition pattern dot. Which side of that trade is better depends entirely on what is already in your safe, which is why the total of 85 against 83 is the least informative number on this page.

The ACRO gap, and what it does not mean

Since the ACRO absence is the P320’s one real restriction, it is worth being precise about its size, because it is easy to overstate.

The ACRO footprint covers 5 optics in this dataset. Zero pistols are cut for it directly. It reaches 80 of the 196 pistols here, all of them through a plate, and those 80 sit on nine plate systems: Glock MOS (16 pistols), S&W M&P CORE (14), FN 509 (12), Walther PDP 2.0 (10), Beretta APX A1 (10), CZ P-10 OR (7), HK VP9 OR (6), Springfield Echelon VIS (4) and Walther PDP 1.0 (1). The P320 X-series plate system is the largest plate system in the dataset that has no ACRO path.

What that does not mean is that a P320 cannot take an enclosed emitter sight. Of the 85 optics a P320 reaches, 16 are enclosed:

• 8 through the RMSc plate, including the Holosun EPS-CORE, both Shield Sights AMS and AMSc, the Meprolight MPO PRO-S, the Primary Arms CLx Enclosed, the Vortex Defender-CCW Enclosed Solar, the Steiner MPS-C and SIG’s own Romeo-X Enclosed Compact.
• 5 through the DeltaPoint Pro plate, including the Bushnell RXE-MR1, EOTech EFLX CE, Vortex Defender-ST Enclosed Solar, Vortex Venom Enclosed and SIG’s Romeo-X Enclosed Pro.
• 3 through the RMR plate: the Trijicon RCR, Meprolight MPO PRO-F and Primary Arms PLx HTX-1.
• 0 through the Docter and C-More STS plates, neither of which carries an enclosed optic at all.

So the honest version of the ACRO gap is narrow: a P320 owner who wants a sealed emitter has 15 options across three plates, but if the specific requirement is an Aimpoint ACRO or a Steiner MPS, this platform cannot do it and no plate in this dataset changes that. It also means the Docter and C-More STS plates, whatever their other merits, are the wrong paths for anyone shopping for a sealed sight.

If you want to put a SIG optic on a SIG pistol

SIG makes red dots as well as pistols, and the obvious assumption is that the house brand mounts cleanly on the house pistol. It does, but not from one plate.

There are 9 SIG Sauer optic pages in this dataset, and they land on exactly two of the five P320 plate paths:

• Five on the RMSc plate: the Romeo-RS Compact, Romeo-X Compact, Romeo-X Enclosed Compact, RomeoZero and RomeoZero Elite.
• Four on the DeltaPoint Pro plate: the Romeo-RS Pro, Romeo-X Pro, Romeo-X Enclosed Pro and Romeo3MAX.

None is on the RMR plate, the Docter plate or the C-More STS plate. The split runs along the size line in SIG’s own naming: the Compact and Zero class sights are RMSc pattern, and the Pro and MAX class sights are DeltaPoint Pro pattern. A P320 owner who wants to stay inside the SIG optics catalogue therefore still has to choose a plate, and choosing the wrong one locks out more than half of SIG’s own lineup.

There is a neat consequence for anyone who carries a P365 and shoots a P320. The five RMSc pattern Romeos mount directly to a P365 slide with no plate at all, and mount to a P320 through the RMSc plate. That is the only way to run one optic model across both SIG pistols without buying two patterns, and it is a real reason to pick the RMSc plate on the P320 even though the RMR plate reaches four more optics.

Picking the plate

Working in this order will get it right on the first try.

1. Start from the optic, never the plate. The plate is a consequence of the optic, and buying a plate first is how people end up with a mount that fits nothing they want. Look up the optic on its own page here, read the footprint off it, and buy the plate that presents that pattern.

2. If you already own a dot, the decision is made. Six of the most common budget open sights sit on the Docter path and nowhere else in this system. A large slice of the Holosun catalogue, 16 of the 33 optics on the RMR path, is RMR pattern. Shield Sights products are RMSc. Look before you shop.

3. If you are starting from nothing and want the widest shelf, take RMR. Thirty-three optics is the largest single path, and it carries the Trijicon RMR Type 2, RMR HD, SRO and RCR plus most of Holosun’s full size line.

4. If you also own a P365 or a SIG 1911, take RMSc instead. It is the only pattern in this dataset that a P320 plate and a direct-cut SIG slide both accept, so one optic model covers both guns. Twenty-nine optics from 11 brands is the widest brand spread of the five paths, and 7 of them are enclosed.

5. If the requirement is a sealed emitter, rule the Docter path out first, and choose between RMSc (7 enclosed) and DeltaPoint Pro (5 enclosed) on brand.

6. If the requirement is specifically an ACRO or a Steiner MPS, this is the wrong pistol and no plate fixes it. That is a platform decision, not a plate decision.

Buy the plate and the optic together where you can, so the screws that arrive are the ones sized for the stack you are actually building. The full cited optic list for any specific model is on that model’s own page, and the complete list of pistols on this plate system is on the plate system hub.

What this dataset does not tell you

Four limits, stated plainly, because a compatibility answer is only as good as its disclosed edges.

The five plate paths trace to a single aftermarket source. All five plate records for this system cite one modular adapter listing rather than a SIG document. The patterns are correct as far as that source goes, but a SIG plate kit page would be better provenance and this system does not have one recorded yet.

No optic dimensions are published here. Window width, window height and weight are absent for all 85 optics on this page. If sight picture size or slide weight is part of your decision, that comparison has to happen on the makers’ own spec pages.

Two records disagree about one pistol. The dataset carries both a “P365 XL” record, listing RMSc only for 30 optics, and a “P365XL” record, listing RMSc plus Holosun K for 35. Those are almost certainly the same pistol under two spellings, sourced from two different pages that disagreed about the Holosun K pattern. Both are shown rather than silently merged, and the conservative reading is the RMSc one. This does not affect any P320 count on this page.

Every pistol here is flagged optic ready, which is an artefact. The dataset only contains optic-ready pistols, so that flag carries no information. It does not mean a pistol arrives ready to take an optic without further parts, and on a P320 it specifically does not: the gun is optic ready and still needs a plate.

The broader version of that last point is the one worth carrying away from any plate system: 84 of the 196 pistols in this dataset, 42.9 percent, have zero direct-fit optics and cannot mount anything at all without a plate. Every P320 here is one of those 84.

Sources

Product and fitment claims above trace to these pages:

• SIG P320 X-series plate paths, all five patterns: outerimpact.com modular red dot adapter for the P320 X5
• P320 M17, M18 and X-Five Legion plate fitment: chpws.com P320 Legion, X-Five, M17 and M18 adapter plate
• P320 XCompact optic-ready configuration: scheels.com P320 XCompact
• P320 XCarry Legion: sigsauer.com P320 XCarry Legion
• P320-XTEN: sigsauer.com P320-XTEN
• Trijicon RMR Type 2 pattern: brownells.com RMR Type 2 RM01
• Leupold DeltaPoint Pro pattern: leupold.com DeltaPoint Pro
• Shield Sights RMSc pattern: shieldsights.com RMSc Reflex Mini Sight Compact
• Burris FastFire 3, Docter pattern: burrisoptics.com FastFire 3
• Vortex Venom, Docter pattern: egwguns.com Vortex Venom footprint
• Aimpoint ACRO P-2, ACRO pattern: aimpoint.us ACRO P-2
• Steiner MPS, ACRO pattern: steiner-optics.com MPS
• Burris FastFire E, ACRO pattern: burrisoptics.com FastFire E
• Holosun HS507C-X2, RMR pattern: holosun.com HS507C-X2

Further reading on this site: do you need an adapter plate, the RMR footprint guide, the RMSc footprint guide, the DeltaPoint Pro footprint guide, and all 24 footprints and plate systems.