SIG P320 Iron Sights & Co-Witness Guide

SIG #6 and #8 sight numbers, front/rear height matching, M17/M18 rear sight plates, suppressor-height sights, optic co-witness, point-of-impact correction, tritium, fiber optic, competition sights, installation, and how to stop guessing which sight set your P320 actually needs.

Sight Numbers   |   Dovetails   |   Co-Witness   |   M17/M18   |   Night Sights   |   Fiber Optic   |   Point of Impact   |   Fitment

P320 sight compatibility looks simple until somebody says, “Just buy SIG #6 front and #8 rear.”

That combination is common across a lot of SIG pistols. It is not a universal P320 rule. SIG's current sight catalog includes #6/#6, #6/#8, #8/#6 and #8/#8 sight sets, and SIG currently sells a P320 X-RAY3 rear sight-plate assembly specified as #8 front / #6 rear. [S2-S4]

Then optics make the problem more interesting. Some P320 slides retain an independent rear dovetail when the optic is installed. Others — including M17/M18-style rear sight plates and some earlier P320 optic-ready systems — place the rear sight on the removable plate. Remove the plate and the factory rear sight leaves with it. [S1][S5]

So the correct question is not “What sights fit a P320?” It is: Which P320 slide do I have, what front/rear geometry does it use now, and what am I trying to accomplish — factory-height replacement, point-of-impact correction, suppressor clearance, competition visibility, or optic backup?

“SIG #6 and #8 are sight-size families — not a magic recipe that every P320 shares.”

SIG uses numbered sight families to identify front and rear sight heights. The number is not the height in inches and should not be treated like a universal “bigger number = taller part” scale.

SIG's current X-RAY3 manual publishes the physical dimensions directly. [S2]

That is why memorizing “#8 is taller” will burn you. It is true for the X-RAY3 rear. It is not true for the X-RAY3 front. Read the actual sight dimensions and match the set intentionally.

“P320 = #6 Front / #8 Rear” Is Not a Rule

#6 front / #8 rear is absolutely a real SIG combination. Ameriglo builds multiple SIG sets around that geometry, and SIG's super-tall suppressor set describes its taller dimensions as the equivalent of #6 front / #8 rear. [S6][S13]

But SIG's own current catalog also offers #6/#6, #8/#8 and #8/#6 combinations. One factory P320 X-RAY3 rear sight-plate assembly is explicitly listed as #8 front / #6 rear. [S3-S4]

Before buying replacement sights, inspect the markings on the existing sights, verify the exact slide/model, and confirm the replacement manufacturer's stated pairing.

Fixed iron sights are geometry. Changing the vertical relationship between the front and rear changes the angle at which the bore is held when the sights look aligned.

For a rough correction estimate:

Example: a 0.020-inch sight-height change across roughly a 6.5-inch sight radius works out to about 2.8 inches at 25 yards. That is useful for understanding why seemingly tiny sight-height changes matter.

Use the equation as geometry, not a substitute for live zeroing. Ammunition, distance, shooter consistency and the exact way a sight's “height” is measured can all affect the real result.

For a conventional fixed rear sight, moving the rear sight to the right moves point of impact right; moving it left moves POI left. Moving the front sight has the opposite effect.

Do not start drifting sights because one three-shot group was off center. Confirm the gun, load and shooter with enough rounds to establish a repeatable group first.

Standard fixed-sight P320 slides use SIG-style dovetails, and SIG's X-RAY3 manual lists the P320 among the pistol families supported by those dovetail sights. [S2]

But aftermarket and optic-ready slides complicate that simple statement. Dawson sells one P320 competition rear for standard fixed rear dovetails and a completely different P320 rear specifically for Grey Ghost Precision slides, with different required front heights. [S11-S12]

That is the shop rule: if the slide is aftermarket, verify the slide manufacturer's sight cut before ordering sights by handgun model alone.

The factory M17/M18 rear sight arrangement is different from a slide with an independent rear dovetail. SIG sells the replacement component as an M17/M18 sight plate and rear sight assembly, because the rear sight and optic-cover plate are one assembly. [S5]

SIG's current P320 manual likewise explains removal of the sight and plate together and notes that M17/M18 models use a single screw to retain the rear sight assembly. [S1]

That means installing an optic on this architecture can remove the factory rear sight along with the plate. Your backup-sight solution may then come from the optic, a dedicated optic/sight system, or a special rear sight designed around that mounting geometry.

Dawson's M17 + DeltaPoint Pro co-witness set is a perfect example: it uses a 0.525-inch rear and 0.400-inch front and specifically warns that the set is not for slides with a separate rear sight dovetail. [S14]

The military-derived ROMEO-M17 uses SIG's SIG-LOC mounting architecture rather than behaving like a generic DPP optic sitting on a normal plate. Its operator manual identifies a rear sight channel and references the M17/M18 pistol rear sight as part of that sighting system. [S9]

Do not use a ROMEO-M17 sight-height answer as a blanket answer for a DPP, RMR, ACRO or ROMEO1PRO mounted on another P320 slide. Same pistol family does not mean same optical centerline.

Whether iron sights appear through an optic window depends on the height of the sights and the optic's optical/deck height above the slide. Adapter-plate thickness adds another variable.

SIG's ROMEO-X PRO is designed around an unusually low deck and SIG explicitly states that it allows absolute co-witness with standard-height iron sights on compatible optic-ready P320-family pistols. SIG makes the same standard-height co-witness claim for the ROMEO-X Enclosed PRO. [S7-S8]

Now compare that with the Dawson M17 + DeltaPoint Pro set: the M17's plate architecture and DPP height require much taller backup irons. [S14]

This is why “What suppressor-height sights work with my P320 red dot?” is incomplete. We need the exact slide, optic, mounting method and desired co-witness height.

Absolute co-witness places the aligned iron-sight picture relatively high in the optic window, often close to the optic's normal centerline. SIG uses that language for ROMEO-X PRO standard-height co-witness. [S7]

Lower-window / lower-third-style co-witness keeps the irons lower in the optic window so they consume less of the red-dot sight picture while remaining visible as backup sights.

Neither is automatically better. Some shooters like a strong, obvious iron reference. Others want the optic window as uncluttered as possible. The mistake is ordering the tallest sights available before deciding what sight picture you actually want.

“Suppressor height” is a category, not a dimensional standard. SIG defines the term generally as sights tall enough to clear a suppressor and notes that tall sights can also serve as optic backup sights. [S15]

SIG's X-RAY3 Super-Tall set measures 0.374 inch at the front and 0.417 inch at the rear and describes that geometry as the equivalent of its #6-front/#8-rear relationship. [S6]

Dawson's M17/DPP co-witness set uses a 0.400-inch front and a substantially taller 0.525-inch rear because it is solving a different slide/optic geometry. [S14]

Buying a product because the listing says “suppressor height” without comparing actual dimensions is the sight equivalent of buying a recoil spring because the package says “competition.”

SIG's X-RAY3 system uses a high-contrast fluorescent front outline around the tritium lamp and subtler rear outlines. The intent is obvious: pull the eye toward the front while still preserving rear reference points in low light. [S2]

That is generally the direction we prefer for a practical iron-sight pistol: the front sight should be the easiest thing to find. Three equally loud white circles can work, but they can also make the sight picture busier than it needs to be.

Sight height controls elevation geometry. Blade and notch width control the visual relationship around the front sight.

A narrower front with more daylight visible on each side can feel faster and make small horizontal errors easier to see. A wider front can be easier for some eyes to pick up and can look more substantial under stress. There is no free lunch — visual speed, precision and visibility trade against each other.

Dawson's standard P320 competition set is a good example of a precision-oriented pairing: 0.200-inch rear height with a 0.135-inch notch and a 0.205-inch-tall, 0.100-inch-wide fiber-optic front option. [S11]

That is a very different sight picture from a thick high-visibility duty front and should be chosen for a reason, not because “competition” sounds better.

Fixed sights: simple, low-profile and durable. Elevation is corrected by selecting the correct front/rear height combination rather than turning a screw.

Adjustable sights: allow windage/elevation tuning without changing fixed sight height. That can be useful for competition, multiple loads or shooters who want to dial a specific zero.

SIG currently offers dedicated adjustable P320 rear assemblies, including the XCarry Legion adjustable night sight and XFive/XFive Legion adjustable systems. [S16]

The tradeoff is obvious: more parts, more height/bulk in some designs and a different fit requirement than a basic fixed dovetail rear.

Changing bullet weight, velocity or load can move point of impact. The difference may be small at close range and more noticeable as distance grows.

If the P320 is an EDC gun, confirm the carry load. If it is a competition pistol, confirm the actual match load. If it is a general-purpose range gun, understand that a fixed iron zero is always a relationship between the pistol, the sight heights, the ammunition and the distance.

Do not “correct” the sights for a load you do not intend to use simply because it happened to be the first box fired after installation.

SIG's X-RAY3 manual recommends professional installation and specifically says the sights are installed from the lead-in side of the dovetail. [S2]

SIG's current replacement-sight product pages go further and classify the work as beyond ordinary field stripping, requiring certified armorer installation for those factory parts. [S17]

Practically, the risk is not mysterious: forcing a hard steel sight through a dovetail in the wrong direction or with poor support can damage the sight, deform the dovetail, mar the slide or leave the sight mechanically loose.

If you are doing sight work in the shop, use a proper sight pusher, verify direction and fit, and do not assume “more force” is the answer when something is obviously wrong.

Mechanical centering is a good starting point. It is not proof of point of impact.

• Confirm the sight is mechanically secure and centered enough to begin.
• Shoot a real group at a known distance from a stable position.
• Use the ammunition the pistol is actually expected to use.
• Correct windage only after the group is repeatable.
• If elevation is consistently wrong, verify the front/rear sight pairing before blaming the pistol.

IronKells P320 Buying Paths

Bottom Line

The P320 does not have one universal iron-sight answer.

Sight number, actual height, front/rear pairing, slide architecture, optic deck height, plate thickness, desired co-witness and point-of-impact correction all matter.

Read the numbers. Measure when necessary. Match the exact slide and optic. Then confirm the zero with the ammunition you actually shoot.

Match the Sight System — Not Just the Pistol Name

Front height, rear height, slide architecture and optic deck all have to agree before “co-witness” means anything.

Sight and optic product lines change. These sources were reviewed October 2, 2026. For replacement parts, verify the exact current slide, sight cut, optic and manufacturer fitment before ordering.

Sight Numbers Are Data. Not Folklore.

Match the geometry, verify the zero, and stop buying sight sets because somebody on the internet remembered one SIG number from fifteen years ago.