Holosun K Footprint vs RMSc: 5 Optics, 26 Pistols Fit

The Holosun K footprint is an RMSc cut with the rear recoil lugs removed: the same two screws, the same front lug positions, two lug positions instead of four. In this dataset it is a five optic pattern from a single brand, milled into 26 of the 196 optic ready pistols here, with one further pistol able to reach it through an adapter plate.

Then there is the fact that makes the whole “K or RMSc” question less dramatic than it sounds: every one of those 26 pistols is also recorded as accepting RMSc optics directly. There is no K only pistol in this dataset. A K cut slide is not a slide with five choices on it. It is a slide with 35.

Every number below is recomputed from the published dataset bundle for this article, version 2026-09-16. The bundle holds 196 optic ready pistols, 100 optic pages covering 135 individual SKUs, and 24 footprint and plate system hubs.

K against the patterns it gets mistaken for

The Holosun K hub owns the current optic list with retail offers. What that page cannot show you, because it is one hub, is where K sits relative to the patterns people put it next to. This table is built across eight hubs, one row each.

Pattern	Optic pages	SKUs	Brands	Screws	Lug positions	Pistols cut for it	Pistols via a plate
Holosun K	5	8	1	2	2	26	1
RMSc	30	33	12	2	4	80	106
RMR	33	47	7	2	2	7	110
DeltaPoint Pro	15	16	5	2	4	2	110
Docter	6	6	4	2	4	0	55
ACRO	5	5	3	clamp	1	0	80
Holosun EPS	1	9	1	2	4	0	0
Holosun 509T	2	8	1	clamp	1	0	0

Three things fall out of that table that are worth more than the individual rows.

K is the only pattern here with real slide adoption and no second supplier. All five K optic pages are Holosun products. RMSc carries 30 pages from 12 brands, RMR carries 33 from 7. Sixteen optic brands appear in this dataset overall, and exactly one of them makes a K pattern optic. That is a supply concentration no other widely cut pattern has: if Holosun discontinues a K model, nothing from another brand steps into the hole. It also explains why the pattern grows on the pistol side much faster than on the optic side. Slide makers keep adding the cut, because the cut is cheap to add next to an RMSc pocket. Optic makers have not followed.

K and RMR record the same screw count and the same lug count. Both are two screws and two lug positions in this dataset, which is exactly why the two get confused in forum answers. They are not close. RMR is a full size pattern carrying 47 SKUs and sitting mostly on duty size slides through plates, 110 of them. K is a micro pattern on carry guns. Counting screws does not separate those two, and this dataset does not publish the screw spacing that would, so the practical test is the size class of the optic, not its underside.

The two other Holosun specific patterns have no pistol cut for them at all. The full size EPS and the 509T each have zero direct fit pistols here and zero plate paths. Whatever those optics mount on, this dataset does not yet record it. K is the only Holosun house pattern in the bundle that a pistol is milled for, and by a wide margin: 26 pistols against 0 and 0.

The finding: there is no K only pistol here

Every one of the 26 pistols cut for K also appears on the RMSc direct fit list. The overlap is 26 of 26. Read from the other side, 80 pistols are cut for RMSc and 26 of those (32.5%) carry the K cut as well, which leaves 54 that do not.

The consequence is a number you can use as a diagnostic. All 26 K cut pistols reach exactly 35 optics: the 30 RMSc optics plus the 5 K optics, with no optic appearing in both groups. The 53 plain RMSc pistols that are not dual cut reach 30. Across all 196 pistols in the bundle, the only ones that reach exactly 35 optics are those same 26. So “35” is a fingerprint. If a pistol page here shows 35 compatible optics, the slide is dual cut, and if it shows 30, it is RMSc only.

The single RMSc pistol that breaks the 30 pattern is the Ruger RXM, which is cut for three patterns at once (RMSc, RMR and DeltaPoint Pro) and reaches 78 optics with no plate. It is the most generous slide in the dataset and it is worth knowing about, but it is not a K gun: none of the five K optics is on its list.

Here is how the 26 distribute by brand. The pistol list itself lives on the hub; this is the shape of it.

Brand	K cut models here
SIG Sauer	10
Canik	4
Taurus	3
FN America	2
Palmetto State Armory	2
Shadow Systems	2
Smith & Wesson	2
Ruger	1

Ten of the 26 are SIG, and all ten are P365 family or P322. That concentration matters when you read a fitment claim online: a great deal of what gets written about “the K footprint” is really written about the P365, and it does not transfer to a Canik MC9 or a Shadow Systems CR920P without checking.

There is a caveat to state plainly, because it is the one place where this dataset’s two layers do not read identically. The footprint record describes the general rule between patterns in isolation: a K cut and an RMSc optic are not interchangeable, and putting a K optic onto an RMSc cut slide calls for an adapter or for modification. The pistol records say something narrower and more specific: on these 26 particular slides, both a K optic and an RMSc optic mount directly, with no plate. Both statements can hold, because a slide can be milled to host either pattern, and because the general rule is about a cut and an optic considered as a pair, not about any one manufacturer’s slide. What you should not do is generalise from the 26 back to the rule. Confirm the pattern for your exact model on the manufacturer’s page before you buy, and treat filing down rear lugs as what it is: a permanent modification to an optic, not a fitment.

How to tell which one you have

Almost every practical mistake with these two patterns is an identification mistake made before the credit card comes out. Four checks, in the order that costs the least.

Check the optic’s model name first. Holosun is unusually consistent here, and the pattern is worth memorising because it resolves most of the confusion on its own. A K in the model number means the K footprint: the 407K-X2 and the 507K-X2. The word Carry in an enclosed model name means the same thing: the EPS Carry, the Ronin EPS Carry and the SCS Carry. A C in the model number means the full size RMR pattern instead: the 407C-X2 and the 507C-X2. That one letter is the difference between 27 pistols and 117 in this dataset.

Then check the slide, from the side, at eye level. With the optic off, look at the rear of the optic pocket. An RMSc cut carries lug detail at both the front and the rear of the pocket, four positions. A K cut carries it at the front only, two positions. On a dual cut slide you will see the RMSc arrangement and a K optic will still sit down in it, which is exactly why looking at the slide alone is not conclusive and why the model name check comes first.

Then read the recoil lugs on the optic underside. Turn the optic over. The K underside has two lug recesses toward the front and a flat rear. An RMSc underside has four, one at each corner. This is the check that cannot be faked, and it is the one that tells you whether the optic in your hand is what the box said.

What you cannot check from this dataset, and should not pretend to. No optic page in the bundle publishes a window width or height: 0 of 100. The footprint records publish screw count and lug count but no screw spacing, no thread size and no boss diameter. So “measure the screw spacing and compare” is not advice this dataset can support with a number, and any page that gives you one without citing a manufacturer drawing is guessing. Where a dimension matters, the manufacturer’s own product page is the source, and for the K series that means Holosun.

Holosun’s own lineup is spread across six patterns

The most useful thing about the K footprint, for a buyer, is not the K footprint. It is that Holosun’s naming convention splits one product family across several mounting standards, and the family name is not the thing to buy on. Of the 27 Holosun optic pages in this dataset, they land on six different patterns: 16 on RMR, 5 on K, 2 on 509T, and one each on RMSc, the full size EPS pattern and two proprietary plate systems.

Holosun optic	Pattern	Pistols it fits here
507K-X2	Holosun K	27
407K-X2	Holosun K	27
EPS Carry	Holosun K	27
SCS Carry	Holosun K	27
507C-X2	RMR	117
EPS Core	RMSc	186
EPS	Holosun EPS	0
509T-X2	Holosun 509T	0

The enclosed emitter line is where this bites hardest, because three products share the letters EPS and mount three different ways. The EPS Carry is K. The EPS Core is RMSc, and that single decision is why it reaches 186 pistols in this dataset while the 507K-X2 reaches 27. The full size EPS is a pattern of its own, described here as the K base with additional front sockets giving four lug positions, and no pistol in the bundle is cut for it.

The SCS line splits the same way but across plate systems rather than footprints: the SCS Carry is K, while the SCS-M is built for the Glock MOS cut and the SCS-PDP for the Walther PDP 2.0 cut. Those two fit 16 and 10 pistols respectively and nothing else. They are the clearest example in the dataset of an optic designed for one platform and stranded there.

The enclosed emitter question

This is the reason most people end up on a K optic in the first place, and the numbers support the instinct. A carry pistol lives in a holster, in lint, in rain, and an open emitter on a micro optic sits close to the slide where debris collects. Enclosed bodies solve that, and the K pattern exists partly because removing the rear lugs is what let Holosun seal the body on the K series.

Across the whole bundle, 27 of the 100 optic pages are enclosed emitter designs. By pattern, the proportions are very uneven:

Pattern	Enclosed of total
Holosun K	3 of 5
ACRO	5 of 5
DeltaPoint Pro	5 of 15
RMSc	8 of 30
RMR	3 of 33
Docter	0 of 6

Three of the five K optics are enclosed: the EPS Carry, the Ronin EPS Carry and the SCS Carry. On the RMR side it is 3 of 33, and that ratio is the real story of the K pattern. RMR is where the selection is; K is where the sealed micro bodies are.

For an owner of one of the 26 dual cut pistols, the practical position is better than either column suggests. Your slide reaches 35 optics, of which 11 are enclosed: the 3 K models plus 8 enclosed RMSc models, among them the EPS Core, the Meprolight MPO Pro S and the Primary Arms CLx enclosed. Nobody with a K cut slide is limited to three sealed optics. They have ten.

The one plate path, and what it costs

Exactly one pistol in the dataset reaches a K optic without a K cut: the Springfield XD-M Elite OSP, through the Springfield XD OSP optic plate in its K variant. That pistol has no direct fit optic at all. Everything it mounts, it mounts through a plate, and across five plates it reaches 89 optics: 33 on the RMR plate, 30 on RMSc, 15 on DeltaPoint Pro, 6 on Docter and 5 on Holosun K.

That single row is a fair illustration of the general trade. A plate system buys breadth, 89 optics against 35, at the cost of a second interface between the optic and the slide and of a part you have to identify correctly before ordering. A dual cut micro slide buys simplicity, one fewer part in the stack, at the cost of the 54 optics the plate systems can reach and it cannot. Which you prefer is a real preference and not a fact, but the sizes of the two numbers are facts.

It is worth naming the 84 pistols in the bundle with zero direct fit optics, because the K owner is in the lucky half. Those 84 are plate system guns: they mount nothing at all until the correct plate is in hand. If that is your situation, the general treatment is in does my pistol need an adapter plate.

What to do with 35 optics

Assume you have confirmed a K cut on a slide that also takes RMSc, which is every K cut pistol here. The decision is no longer about footprints, so stop shopping by footprint and start shopping by the three things that actually differ across the 35.

Sealed or open. Eleven of the 35 are enclosed, as above. If the gun is carried daily, this is the first filter, and it is the one that most often sends buyers to a K optic even though seven of the ten sealed options are RMSc.

Window size and dot size. This dataset publishes neither window dimension for any optic, so use the manufacturer’s page. That is a real limit and stating it is more useful than inventing a comparison. What the dataset can tell you is which manufacturer page to open, and the optic pages carry those links.

Availability, not rank. There is no “best” column in this dataset and there is not going to be one. What exists is 35 optics, each with the retailers carrying it. Popularity is not a compatibility fact.

Two checks before ordering, both cheap:

1. Open your pistol’s page here and read the accepted patterns line. If it lists both Holosun K and RMSc, your optic list is the full 35 and any K model will sit directly on the slide. Ruger MAX-9, SIG P365XL and Taurus GX4 TORO all read this way, as do the other 23.
2. Confirm against the manufacturer. Slide cuts change between generations and between variants of the same name more often than model pages admit, and this dataset records what its sources record. Of the 100 optic pages here, 41 are flagged verified against a manufacturer page; none of the five K optics is among them yet. That is our gap, not yours, and it is being closed record by record, but until a page carries the flag the manufacturer’s own listing is the higher authority.

Where the K pattern does not go

The pattern’s reach is narrow and the shape of the narrowness is specific. 27 of 196 pistols here can mount a K optic at all, 26 by direct cut and 1 through a plate. The other 169 cannot, and they cannot for two different reasons that are worth telling apart.

Most of them are plate system guns cut for a proprietary pocket: Glock MOS, SIG P320 X-series, S&W M&P CORE, the rest of the 15 plate systems in the bundle. Those pistols can reach the RMR, RMSc, DeltaPoint Pro, Docter and ACRO patterns through plates, but no plate in this dataset presents the K pattern on any of them except the Springfield XD OSP. This is not a claim that no such plate exists anywhere in the world. It is a claim about what is recorded here, and the honest version is the second one.

The rest are duty size pistols cut directly for RMR or RMSc, where a micro optic is simply the wrong size class. A K optic on a full size slide leaves the rear of the pocket unsupported and the window undersized for the sight radius. Nothing in this dataset prevents the combination; physics and good sense do.

If your pistol is in the 169, the two paths are the plate route, covered on your pistol’s page and on the relevant plate system hub, or a different optic pattern. For most duty size guns that means RMR with 33 optics from 7 brands, which is the deepest bench in the bundle, or RMSc with 30 from 12 brands if the slide is cut for it.

What this dataset does and does not claim

Every fit above comes from the bundle, and the bundle is explicit about its own edges. It records 196 optic ready pistols, which is a filtered population and not the whole handgun market: a pistol with no optic cut and no plate system never enters it. It records 100 optic pages standing in for 135 SKUs, because colour, reticle and battery variants of the same body share a mounting pattern and do not deserve separate answers. Of those 100, 41 are flagged verified against a manufacturer source today. It publishes no window dimensions and no screw spacing for any pattern.

What it does claim, and will stand behind, is the mounting relation: which optic mounts on which pistol, directly or through a named plate, with the source for each relation attached to the record. For the K pattern that comes to 5 optics, 26 pistols by direct cut, 1 by plate, and 35 optics on every one of those 26 slides. The Holosun K hub carries the current lists with retail offers, and the RMSc hub carries the other 30.

If you want the wider comparison between the two patterns’ parent standards, RMSc vs RMR covers the 30 against 33 case, and the RMSc footprint guide covers what RMSc is on its own terms.

Sources

Product and pattern claims above are cited inline. The manufacturer and retailer pages used:

• Holosun 407K-X2, 507K-X2 and SCS Carry product pages, for the K series models.
• Holosun 407C-X2 and 507C-X2, for the full size RMR pattern siblings.
• Holosun EPS and EPS Core, for the enclosed line split.
• The EPS Carry mounting guide, for the EPS Carry footprint.
• Holosun SCS-M and SCS-PDP, for the platform specific SCS variants.
• The Springfield XD OSP optic plate listing, for the single K plate path.
• Meprolight MPO Pro S and the Primary Arms CLx enclosed reflex sight, for enclosed RMSc options.
• The OpticsPlanet guide to the Holosun K footprint, for the pattern description.
• Pistol level fitment in this dataset traces to manufacturer specification sheets and to Swampfox’s RMSc compatible handgun list; each pistol page shows the source attached to its own record.