SIG P320 Holster Compatibility & Fitment Guide

Full Size, Carry, Compact, XCompact, M17, M18, XCarry, XFive, optics, weapon lights, comps, manual safeties, thumb rests, grip modules, retention systems, and the fitment details that decide whether a holster actually works.

Model Length   |   Grip Modules   |   Optics   |   Lights   |   Comps   |   Gas Pedals   |   Retention   |   Duty & Concealment

The phrase “fits SIG P320” is almost useless by itself.

The P320 family spans multiple slide and barrel lengths, different grip-module shapes, manual-safety and non-safety configurations, optics, weapon lights, suppressor-height sights, integrated and threaded compensators, oversized takedown levers, gas pedals, magwells and heavy competition frames. A holster molded for one combination can fit another perfectly, fit loosely, bind, lose retention, expose too much trigger area, block a control, or simply stop the pistol before it fully seats.

Major holster makers prove the point themselves. T.REX currently separates P320 support into distinct 3.6-inch, 3.9-inch, 4.7-inch and 5.0-inch families, while Safariland publishes specific P320 fits for Full Size/M17, M18/XCarry, XCompact and XFive-style configurations. [S3][S9-S10]

The right way to buy a P320 holster is to identify the whole gun as carried — not just the FCU family stamped on the box.

“The FCU makes it a P320. The outside dimensions determine whether it fits the holster.”

Holster manufacturers do not all use SIG's model names the same way, so barrel/slide length is the cleaner starting point.

SIG's current M17/M18 manual lists the M17 at 4.7 inches and the M18 at 3.9 inches, with overall lengths of about 8.05 and 7.25 inches respectively. Those dimensional differences are large enough that “M17/M18 holster” should never be assumed unless the manufacturer explicitly says the shell accommodates both. [S2]

A P320 holster usually interacts heavily with the slide, trigger guard, accessory rail and sometimes the ejection-port area. Swapping from one grip module to another can be invisible to the holster — but only when those contact surfaces remain close enough to the original geometry.

Standard polymer, X-Series, TXG, AXG and aftermarket modules can differ in rail length, dust-cover profile, trigger-guard shape, width and accessory geometry. A custom module can still use the same FCU and magazine while no longer matching the shell molded around the old module.

If the holster manufacturer lists your specific module or family, use that answer over internet folklore. Safariland's safety warning says modified guns and aftermarket grip-related changes can cause improper fit when the holster was not designed around them. [S5]

The military-pattern M17/M18 family uses external manual-safety levers, and SIG's M17/M18 documentation shows the safety-equipped geometry as part of the platform. [S2]

Some holsters have enough clearance that the safety makes no difference. Others mold tightly around the upper grip/FCU area and may require the M17/M18-specific shell. This is one reason manufacturers sometimes list “P320 Carry,” “M18,” and “XCarry” separately even though the slides may share a 3.9-inch length.

Treat the safety like any other external control: if the maker does not explicitly support it, verify before ordering.

An optic-ready holster needs enough clearance behind the ejection port for the optic body and enough room for the pistol to seat without the optic contacting the shell or hood.

Safariland's 7TS RDS family was specifically released in P320 fits including P320RX, XFive/Full Size/VTAC/M17, M18/XCarry and XCompact — which shows how both optic clearance and pistol family are part of the fit definition. [S10]

Large optics can still create exceptions. T.REX's current listing for the Safariland 6354 optic-compatible holster identifies several compatible red dots and notes that the SRO requires holster modification, which voids the duty rating. [S12]

“Optic cut” does not mean “every optic ever made.” Check the specific optic when the holster uses a protective hood, ALS geometry or close molding around the optic pocket.

A non-light-bearing Kydex holster can usually mold tightly around the trigger guard because nothing larger than the guard has to pass through the mouth of the shell.

A weapon-mounted light changes that geometry. PHLster explains that many pistol lights are wider than the trigger guard, so the lower portion of the holster must open wide enough for the light to enter. That prevents traditional trigger-guard retention and is why many light-bearing holsters retain on the light body instead. [S6]

• The exact light matters. An X300, TLR-1 HL and TLR-7 are not interchangeable retention surfaces just because all three attach to a P320 rail.
• Some trigger-area gap is often unavoidable. The shell has to pass over the wider light body. The important question is whether that gap is minimized and appropriate for the exact gun/light design.

T.REX's current P320 support map shows separate light combinations for each P320 length family, including X300, TLR-1 and TLR-7-family lights. [S9]

Trigger Protection Still Matters

PHLster's safety guidance is straightforward: a holster should protect the trigger with rigid material, but light-bearing holsters will have some gap near the trigger because of the light geometry. They specifically warn users to keep drawstrings, clothing and other objects out of that opening while holstering. [S7]

This is not theoretical. Safariland has issued service bulletins for particular duty holster/light combinations where retention or safety behavior did not meet specifications, including a 2021 bulletin involving right-handed 7TS Gen 2 P320/P320C holsters used with SureFire X300-family lights and a separate bulletin covering TLR-7-size duty holsters. [S4]

The lesson is not “light-bearing holsters are unsafe.” The lesson is that exact fit, retention testing and manufacturer updates matter.

PHLster's Floodlight2 indexes and retains on a specific full-size light such as an X300 or TLR-1 family light and uses adjustable slide contact to support multiple pistols. [S8]

Tier 1's MSP line follows a similar light-centric idea and lists a broad range of P320 models including P320, X5, M17, M18, XCarry, Full Size and VTAC. [S13]

That can be useful for owners with multiple pistols, but “universal” never means “ignore fit.” PHLster specifically warns that modified pistols may fit differently or not at all and tells users to confirm modifications before relying on the setup. [S8]

A threaded barrel adds muzzle length. A compensator adds more. Closed-bottom holsters can stop the gun before it reaches normal retention, while open-ended shells may allow extra length to pass through.

Open muzzle alone does not guarantee fit. A compensator can be wider or taller than the slide and may collide with the holster body during insertion. An integrated-comp slide can have a different front profile from a normal slide.

If you are carrying a comped P320, order around the actual compensated configuration or get explicit confirmation from the holster maker. Safariland warns users not to assume modified guns will fit an unmodified-gun shell. [S5]

The P320's removable takedown lever made thumb-rest upgrades easy, but it also puts the modification directly on the side of the gun where many holsters are closely molded.

GoGun's current P320 Gas Pedal page says the part adds roughly a quarter-inch of width and fits many holsters, while acknowledging that tight-fitting designs may require minor modification. [S11]

For a competition shell intentionally cut for the pedal, no problem. For a duty-rated retention holster, do not start melting, grinding or cutting the shell because a forum post says it works. Safariland explicitly warns not to modify its products and says aftermarket firearm changes can produce improper fit. [S5]

If the thumb rest matters to the build, make the holster part of the build plan from day one.

The internet loves the upside-down shake test because it makes a dramatic video. It is not a universal retention standard.

PHLster specifically tells users to test retention while the holster is worn because belt/body compression changes the shell's behavior. Its guidance describes a properly adjusted holster as one that keeps the pistol in place through vigorous movement while still releasing cleanly during an intentional draw. [S6]

For active-retention duty holsters, follow the maker's actual retention test and inspection procedure.

Sometimes. If the retention point and critical molding are shared between shorter and longer slide families, the shorter gun may seat correctly with unused space near the muzzle. Some manufacturers deliberately design families this way.

Another holster may use muzzle position, ejection port, slide length or accessory geometry as part of its lockup. Then the shorter gun can sit too deep, fail to engage retention or move excessively.

Never infer this from barrel length alone. Use the manufacturer fit list for that exact holster model.

The serialized FCU is why the same firearm can become an XCompact today and a Full Size tomorrow. The holster does not care which serialized FCU is inside it. It only sees the outside shape.

With the firearm unloaded and ammunition out of the work area, verify the actual mechanical fit first.

• Pistol seats to the intended depth without being forced.
• Trigger area is protected as designed and no object can easily access the trigger.
• Retention engages consistently every time.
• Active release moves normally and does not bind.
• Optic, sights, safety levers, slide catch, gas pedal and comp clear the shell.
• Weapon light does not shift or unlock on insertion/draw.
• Holster hardware is tight and attachment is secure.
• Retention still feels correct when the holster is worn on the actual belt/chassis. [S6]

Kydex is workable material, and competition/range shooters modify shells all the time for gas pedals, comps or unusual controls. That does not make every modification smart.

Before altering a shell, ask what that area does. Is it just cosmetic clearance? Is it a retention surface? Does it protect the trigger? Does an ALS component depend on that geometry? Is it part of a tested duty system?

Safariland's current warning is unambiguous: do not modify its holsters, and aftermarket firearm modifications can create improper holster fit when the holster was not designed around them. [S5]

IronKells P320 Buying Paths

Bottom Line

P320 holster compatibility is not hard once you stop treating “P320” as one exterior shape.

Identify the slide length. Identify the grip module. Add the manual safety if present. Name the exact light. Name the optic. Include tall sights, threaded barrel, comp, gas pedal and any other part that changes the outside of the gun.

Then buy the holster for the gun you actually built — not the model name you started with.

Fit the Holster to the Entire Weapon System

Slide, frame, light, optic, controls, comp and carry role all matter. Get the combination right once instead of buying a drawer full of almost-fitting plastic.

Fitment data changes as holster makers add or discontinue molds, lights and optics. These sources were reviewed October 2, 2026. Use the manufacturer fit selector for the exact configuration before ordering.

Build the Gun. Then Fit the Holster to That Gun.

Because “P320 compatible” is a hell of a lot less useful when your P320 has an AXG grip, X300, enclosed optic, gas pedal and compensator.