SIG Sauer P320

easy
Shop tier 1
medium confidence
Pistol
striker fired
modular
serialized chassis
no trigger pull takedown
duty pistol

field strip ~1 min · reassembly ~1 min · detail strip ~15 min

Before you begin Verify this firearm is unloaded. Remove the magazine or empty the cylinder or tube, lock the action open, and check the chamber both by sight and by touch. Keep the muzzle in a safe direction and remove all live ammunition from your work area.

SIG Sauer safety notice · 2017 · upgrade available P320 Voluntary Upgrade Program. Affected: All SIG SAUER P320 pistols purchased before August 2017, i.e. without the upgraded trigger, sear, striker and mechanical disconnector; P320s made after 2017-08-08 already include the upgraded design. SIG's online serial-number lookup shows whether a given pistol has been upgraded. Hazard: SIG states the upgrade 'will enhance the protection against unintended discharges if the pistol is dropped' and that any unintended discharge, including from a dropped firearm, carries a risk of death or serious bodily injury; the added mechanical disconnector also protects against cartridge-failure events and prevents a dead trigger if the trigger is pulled with the slide retracted. What the maker asks: Voluntary, free upgrade (SIG pays shipping both ways): register online at sigsauer.com/support/p320-voluntary-upgrade/ (serial-number lookup) or call SIG SAUER Customer Service (603) 610-3000 option 1; the pistol is returned with lighter trigger/sear/striker and a mechanical disconnector. (SIG SAUER — Voluntary Upgrade Notice (P320 upgrade program customer letter) — SIG SAUER, Inc. sigsauer.com [8])

SIG Sauer limits owner disassembly The maker's own procedure goes as far as: Field strip, magazine disassembly, and the section 8 user procedures, including removing the Fire Control Unit from the grip module. The FCU itself is not to be disassembled.. SIG says not to disassemble the P320 beyond the point explained in the manual; further disassembly is restricted to a certified SIG SAUER armorer or professional gunsmith, and ignoring this voids the warranty. No further disassembly of the FCU is authorized. (SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 5 sigsauer.com [3])

Specifications

Manufacturer: SIG Sauer
Origin: United States
Category: Pistol
Action: Striker-fired, short recoil
Calibers: 9x19mm Parabellum, .40 S&W, .357 SIG, .45 ACP
Capacity: 17+1 in 9mm full size
Production: 2014–present (in-production)
Also known as: M17, M18, P320 X-Carry, P320 Compact

Model-specific safety

No trigger press is required to field strip this pistol. If you find yourself about to press the trigger to take it apart, stop — you are doing it wrong.
The serialized component is the internal fire control unit, not the frame or slide. Handling the fire control unit is handling the firearm itself for legal purposes.
SIG Sauer ran a voluntary upgrade program for P320 pistols made before roughly August 2017, addressing drop-related discharge concerns. If you own an early pistol and do not know its upgrade status, contact SIG Sauer before carrying or disassembling it.
The recoil spring assembly is under tension when the slide is off.

Under spring tension

Recoil spring assembly

Easily lost parts

Takedown lever · Fire control unit rails

Tools

No tools required for the field strip.

Shop difficulty

Shop tier 1 Tier 1 — easy among pistols, for the full job: strip to the parts that get coated and put it back together working. The coatable parts come off as units: the fire control unit lifts out of the polymer grip module in the owner procedure and stays assembled (SIG reserves the sear housing for depot), leaving a slide with striker, extractor and sights. Only order matters (slide off before the takedown lever).

No sourced part count yet.

Bench time: about 15 min to strip, 20 min to rebuild (estimate). Slide (striker assembly, extractor, sights, optic plate) and FCU out of the grip module as a unit; rebuild is striker and FCU back in plus function check.

What comes off for coating

Slide: slide cover plate, striker assembly, extractor, spring and pin, rear sight, front sight — pin punch, sight pusher
Grip module / FCU: takedown lever, fire control unit (as a unit), slide catch lever and spring (if FCU opened) — 90-degree pick

Special tools

90-degree pick — Takedown safety lever spring
FCU support block (e.g. Gray Guns) — Driving the sear housing pin if the FCU is opened
dovetail sight pusher (or brass drift and padded vise) — Removing and refitting dovetailed sights for coating

Known pain points

If the takedown lever is pulled before the slide is off, the fire control unit lifts out with the slide and the two lock together. (disassembly)
Owners report: Seeking stupidity relief: P320 FCU stuck on slide. (Don't remove the takedown lever first!) - Topic — SIGforum sigforum.com [14] — “If one removes the P320 takedown lever before removing the slide, the fire control unit comes along with the slide when it’s lifted up, and then they can’t be separated.”
If the FCU itself is opened, every pin pushes except the sear housing spirol pin, which must be driven with the unit supported, and the takedown safety lever spring needs a 90-degree pick. (both)
Owners report: Building a P320 FCU from parts - Topic — SIGforum sigforum.com [15] — “All P320 pins push in easily except for the Spirol (roll) pin that must be driven through the Sear Housing.”
SIG restricts disassembly past the manual to its armorers or a professional gunsmith. (both)
Source: SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER sigsauer.com [3] — “Disassembly beyond the instructions in this manual is restricted to a certified SIG SAUER armorer or professional gunsmith.”

Fit or check on rebuild

FCU fully seated in the grip module — A partly seated FCU gives a gritty trigger or no reset
Function check: trigger reset, sear/striker engagement, safeties — Standard post-reassembly check on any pistol whose fire-control parts were removed; a mis-seated spring shows up here, not on the bench

This is Pew-Takedown's rating, not the manufacturer's. How tiers are rated. Forum reports are owners' experience, not specifications.

Manufacturer videos

Official videos from SIG Sauer's own channels, linked rather than copied. Where a video and the steps on this page differ, follow the manufacturer's manual and video.

P320 Field Strip and Cleaning with Chris Cavallaro SIG SAUER Academy field strip, cleaning, maintenance, reassembly · 2021-05-20

Procedures

Clear and Make Safe

Clear & Make Safe

Point the muzzle in a safe direction and keep your finger off the trigger.
Press the magazine release and remove the magazine.
Removed at this step: Magazine
Retract the slide fully and lock it open with the slide catch lever.
Visually and physically verify the chamber is empty.
Remove all live ammunition from the work area.

Field Strip

No trigger press required — the takedown lever is reachable with the slide locked back.

Manufacturer’s video: P320 Field Strip and Cleaning with Chris Cavallaro SIG SAUER Academy

Complete the Clear and Make Safe procedure and leave the slide locked to the rear.
Rotate the takedown lever on the right side of the frame downward about 90 degrees until it stops.
TipOn some pistols the lever is stiff when new. Thumb pressure, not tools.
Hold the slide, release the slide catch lever, and ease the slide forward off the frame.
Removed at this step: Slide assembly
Lift the recoil spring assembly out of the inverted slide.
WarningIt is under spring tension — keep a thumb on it.
Removed at this step: Recoil spring assembly
Lift the barrel up and out of the slide.
Removed at this step: Barrel

Remove the Fire Control Unit

Detail Strip

The step that makes the P320 modular. The fire control unit is the serialized firearm.

Field strip the pistol and set the slide, barrel, and recoil spring assembly aside.
With the takedown lever still rotated down, grasp the takedown lever and lift the fire control unit up and out of the grip module.
TipIt lifts out rear-first on most grip modules.
Removed at this step: Fire control unit
To install into another grip module, seat the front of the fire control unit first, then press the rear down until it sits flush.
Confirm the fire control unit is fully seated and the takedown lever rotates freely before reassembling the slide.
WarningA partially seated fire control unit can bind the trigger. Verify with a function check.

Reassembly

Manufacturer’s video: P320 Field Strip and Cleaning with Chris Cavallaro SIG SAUER Academy

Set the barrel into the inverted slide and seat it fully forward.
Seat the recoil spring assembly into the cut in the barrel lug and press it down into the slide channel.
Set the slide onto the frame rails and push it rearward until the slide catch lever will lock it open.
With the slide locked back, rotate the takedown lever up to horizontal.
Release the slide and perform the function check.

Torque specifications

Use a calibrated torque driverValues are the manufacturer's, shown in the unit it gives first; conversions are calculated and rounded. Tighten to the stated value — not "until it feels right" — and follow any sequence noted.

Fastener	Torque	Sequence, notes and the source's words	Where it comes from
Sight plate screws (2, rear sight/sight plate, 3/32 in. hex, from bottom of slide) SIG P320 pistols	20 in-lb 2.3 N·m · 1.7 ft-lb	Install LCI post and spring into slide; install sight plate and sight onto slide holding LCI post and spring in place; insert sight plate screws from bottom of slide and tighten to 20 in-lbf; then reinstall striker assembly, extractor, extractor pin/spring/plus pin and rear slide cap. Note: 'Sight plate screws are for securing the rear sight and sight plate only.' 8.1 table also lists 20 in-lbf / 2.26 nm. Threadlocker: LOCTITE 243 (per 8.1 table; 'If there is no Nylok® patch present on the fastener, use specified Loctite®') “3. Insert sight plate screws into the bottom of slide and tighten to 20 in-lbf using a 3/32 in. Hex drive bit.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 81 sigsauer.com [3]
Blanking (optic cover) plate screws (2, T20, top of slide) SIG P320 optic-cut slides	20 in-lb 2.3 N·m · 1.7 ft-lb	Place blanking plate into its slot in slide; insert blanking plate screws and tighten. Note: 'Blanking plate screws are for securing the blanking plate only.' CONFLICT: the section 8.1 torque table (p. 77) lists Blanking Plate Screws at 25 in-lbf / 2.82 nm. Threadlocker: LOCTITE 243 (per 8.1 table; 'If there is no Nylok® patch present on the fastener, use specified Loctite®') “2. Insert blanking plate screws and tighten to 20 in-lbf using a T20 drive bit.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 85 sigsauer.com [3]
ROMEO red dot mounting screws (2, 1/8 in. hex) SIG P320 pistols equipped with a SIG ROMEO optic (with or without shroud)	25 in-lb 2.8 N·m · 2.1 ft-lb	Insert ROMEO into shroud (if equipped); place ROMEO and shroud assembly on slide aligning holes; install ROMEO screws and torque to 25 in-lbs; refer to ROMEO manual for zeroing. 8.1 table also lists 25 in-lbf / 2.82 nm. Threadlocker: LOCTITE 243 (per 8.1 table; 'If there is no Nylok® patch present on the fastener, use specified Loctite®') “3. Install ROMEO screws with 1/8 in. Hex drive bit and torque to 25 in-lbs.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 88 sigsauer.com [3]
Compensator attachment screws (2, T10) SIG P320 models with factory barrel compensator	20 in-lb 2.3 N·m · 1.7 ft-lb	Clean and degrease threads of barrel and compensator. Insert barrel into slide. Apply LOCTITE 246 to threads of barrel and compensator. Thread compensator onto the barrel until it stops, then unscrew until vertical slots in barrel align with the screw holes in the compensator. Install compensator attachment screws and apply a final torque of 20 in-lbf. (8.1 table: Barrel Compensator Threads N/A torque, LOCTITE 246.) Threadlocker: LOCTITE 243 on screws; LOCTITE 246 on barrel/compensator threads (8.1 table) “4. Install compensator attachment screws into compensator using a T10 drive bit and apply a final torque of 20 in-lbf.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 94 sigsauer.com [3]
Magazine funnel screw, standard funnel (T10, rear of grip module) SIG P320 grip modules with detachable standard magazine funnel	6 in-lb 0.68 N·m · 0.5 ft-lb	Threadlocker: LOCTITE 243 (per 8.1 table; 'If there is no Nylok® patch present on the fastener, use specified Loctite®') “For standard magazine funnel screw, use a T10 drive bit to thread funnel screw into rear of grip module and tighten to 6 in-lbf.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 100 sigsauer.com [3]
Magazine funnel screw, AXG magazine well (T10, bottom of grip module) SIG P320 AXG grip modules	11 in-lb 1.2 N·m · 0.92 ft-lb	Threadlocker: LOCTITE 243 (per 8.1 table; 'If there is no Nylok® patch present on the fastener, use specified Loctite®') “For AXG magazine funnel screw, use a T10 drive bit to thread funnel screw into bottom of grip module and tighten to 11 in-lbf.”	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER, p. 100 sigsauer.com [3]

Notes: SIG's P320 manual gives two figures for the blanking (optic cover) plate screws: 25 in-lbf in its torque table and 20 in-lbf in the installation step. The installation step's 20 in-lbf is shown; confirm with SIG if it matters for your slide.

Reported by other sources — not the manufacturer

Not a manufacturer specificationThese values come from the people and publications named beside each one, not from SIG Sauer, and where they differ from the manufacturer's values above, the manufacturer wins. They are recorded with who said them and their exact words so you can judge them — not as a recommendation. Confirm any of them with the manufacturer or a licensed gunsmith before you put a wrench on your firearm; a wrong value can crack a stock, strip a thread or loosen a muzzle device.

Fastener	Torque	Who says so, and their words	Where it comes from
Optic mounting screws through plate (T15 6-40 x 9/16) SIG P320 (not M17/M18, not integrated-plate slides) with Forward Controls Design OPF-P320, RMR plate, Trijicon RMR	13–15 in-lb 1.5–1.7 N·m · 1.1–1.2 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher “Torque value for T15 6-40 x 9/16 screws: 13 to 15 in lb.”	OPF-P320, RMR (product page) — Forward Controls Design forwardcontrolsdesign.com [4]
Optic plate to slide screws SIG P320 X-Five Legion, Legion Carry, commercial M17/M18 and Romeo1 Pro/DPP-cut slides with FCD OPF-P320, RMR, RSD plate	12 in-lb 1.4 N·m · 1 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher “Plate to slide: 12 in·lb”	OPF-P320, RMR, RSD (product page) — Forward Controls Design forwardcontrolsdesign.com [5]
Optic (sight) to plate screws SIG P320 R1P/DPP-cut slides with FCD OPF-P320, RMR, RSD plate, Trijicon RMR	12 in-lb 1.4 N·m · 1 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher “Sight to plate: 12 in·lb”	OPF-P320, RMR, RSD (product page) — Forward Controls Design forwardcontrolsdesign.com [5]
Optic plate to slide screws (M4 x 0.7 x 6 mm) Military-issue M17/M18 (P320 variant) with Forward Controls Design OPF-M17, ACRO plate	20 in-lb 2.3 N·m · 1.7 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher Threadlocker: VC-3 packet supplied “OPF-M17-ACRO is shipped with two M4 0.7mm x 6mm (torque value: 20 in·lb) and a packet of VC-3.”	OPF-M17, ACRO (product page) — Forward Controls Design forwardcontrolsdesign.com [6]
Aimpoint ACRO P1/P2 mounting screw Military-issue M17/M18 with FCD OPF-M17, ACRO plate, Aimpoint ACRO P1/P2	26 in-lb 2.9 N·m · 2.2 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher “Torque value for ACRO P1/P2 mounting screw: 26 in·lb. For Steiner MPS, 18 in·lb. (updated by Steiner in 2024)”	OPF-M17, ACRO (product page) — Forward Controls Design forwardcontrolsdesign.com [6]
Steiner MPS mounting screw Military-issue M17/M18 with FCD OPF-M17, ACRO plate, Steiner MPS	18 in-lb 2 N·m · 1.5 ft-lb	Reported by Forward Controls Design Secondary — a parts or tool maker, or a gunsmithing publisher “Torque value for ACRO P1/P2 mounting screw: 26 in·lb. For Steiner MPS, 18 in·lb. (updated by Steiner in 2024)”	OPF-M17, ACRO (product page) — Forward Controls Design forwardcontrolsdesign.com [6]
Optic adapter plate mounting screws (Holosun RMR-footprint plate for P320 Romeo1 Pro cut) SIG P320 with Romeo1 Pro optic cut, HOLOSUN adapter plate for RMR footprint (407C/507C/508T/SRO)	1.4 N·m 12 in-lb · 1 ft-lb	Reported by HOLOSUN Europe (holosun.eu, operated by Picotronic GmbH, HOLOSUN European distributor) Secondary — a parts or tool maker, or a gunsmithing publisher “Tightening torque recommended: 1,4 Nm”	Adapter plate for Footprint RMR on SIG P320 Romeo 1 Pro (product page) — HOLOSUN Europe (holosun.eu, operated by Picotronic GmbH, HOLOSUN European distributor) holosun.eu [7]
Optic adapter plate mounting screws (Holosun RMR-footprint plate for P320 Romeo1 Pro cut) SIG P320 with Romeo1 Pro optic cut, HOLOSUN adapter plate for RMR footprint (407C/507C/508T/SRO)	max. 1.7 N·m 15 in-lb · 1.3 ft-lb	Reported by HOLOSUN Europe (holosun.eu, operated by Picotronic GmbH, HOLOSUN European distributor) Secondary — a parts or tool maker, or a gunsmithing publisher “tightening torque Maximum: 1,7 Nm”	Adapter plate for Footprint RMR on SIG P320 Romeo 1 Pro (product page) — HOLOSUN Europe (holosun.eu, operated by Picotronic GmbH, HOLOSUN European distributor) holosun.eu [7]
Red-dot optic mounting screws (6-32 flat head, supplied) into EGW rear-dovetail sight mount SIG Sauer P320 (non-optics-ready slide with rear dovetail) with the EGW 'Trijicon RMR / SRO, Holosun 407c / 507c Mount for Sig Sauer P220, P226, P229, P320' (replaces the rear sight; for Trijicon RMR/	15 in-lb 1.7 N·m · 1.2 ft-lb	Reported by Evolution Gun Works (EGW) Secondary — a parts or tool maker, or a gunsmithing publisher Remove the rear sight, install the EGW mount in the dovetail, tighten the set screw if applicable, place the optic on the mount, then apply blue Loctite and torque the optic screws. Threadlocker: Blue Loctite on the provided mounting screws (EGW instructions) “Torque mounting screws to 15in/lbs”	Trijicon RMR / SRO, Holosun 407c / 507c Mount for Sig Sauer P220, P226, P229, P320 (EGW product page, installation instructions section) — Evolution Gun Works (EGW) egwguns.com [11]
Red-dot optic mounting screws (supplied) into EGW rear-dovetail sight mount (Docter/Venom/Viper/FastFire footprint) SIG Sauer P320 (non-optics-ready slide with rear dovetail) with the EGW 'SIG Sauer P220 P226 P229 P320 Red Dot Mount \| Fits Vortex Venom, Viper & Burris FastFire \| EGW' (replaces the rear sight)	15 in-lb 1.7 N·m · 1.2 ft-lb	Reported by Evolution Gun Works (EGW) Secondary — a parts or tool maker, or a gunsmithing publisher Remove the rear sight, install the EGW mount in the dovetail, tighten the set screw if applicable, place the optic on the mount, then apply blue Loctite and torque the optic screws. Threadlocker: Blue Loctite on the provided mounting screws (EGW instructions) “Torque mounting screws to 15 in/lbs”	SIG Sauer P220 P226 P229 P320 Red Dot Mount \| Fits Vortex Venom, Viper & Burris FastFire \| EGW (EGW product page, installation instructions section) — Evolution Gun Works (EGW) egwguns.com [12]
Vortex Venom mounting screws on EGW adapter plate (Romeo1-cut optics-ready slide) SIG Sauer P320 RX / P320 X-Five Optics Ready (Romeo1 cut; not M17 or Romeo1 Pro cut) with the EGW 'Adapter Plate for Sig P320 (Romeo) to Vortex Venom'	15 in-lb 1.7 N·m · 1.2 ft-lb	Reported by Evolution Gun Works (EGW) Secondary — a parts or tool maker, or a gunsmithing publisher Threadlocker: Blue Loctite on the provided mounting screws (EGW instructions) “Torque Specs: 15 in/lbs”	Adapter Plate for Sig P320 (Romeo) to Vortex Venom (EGW product page, installation instructions section) — Evolution Gun Works (EGW) egwguns.com [13]

Materials and factory finish

As stated by SIG Sauer. Prep, masking and cure depend on these; a polymer or aluminium part, a nitrided or anodised finish, and a blued steel part are each a different job. Variants with other finishes may exist — check the maker's page for the exact SKU on the bench.

Component	Material	Factory finish	Where it comes from
Grip module all P320 models (manual 13.0)	Glass reinforced	—	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER sigsauer.com [3] “Glass reinforced grip module or, alloy steel with integral accessory rail.”
Grip module P320 models with a metal grip module (models not named)	alloy steel	—	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER sigsauer.com [3] “Glass reinforced grip module or, alloy steel with integral accessory rail.”
Slide all P320 models (manual 13.0)	stainless steel	—	SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER sigsauer.com [3] “Solid high-strength stainless steel slide with front and rear cocking serrations.”
Frame (serialized fire-control unit) P320	Stainless Steel	—	SIG SAUER, Inc. — 2019 GDS CATLOG WORKING FINAL LR — SIG SAUER, Inc. sigsauer.com [9] “Serialized Stainless Steel Frame”
Whole firearm P320 Full Size, item 320F-9-B	—	NITRON The maker states this for the firearm as a whole, not for a named part.	SIG SAUER, Inc. — 2021 Guide Price List 11 8 — SIG SAUER, Inc. sigsauer.com [10] “P320, 9MM, 4.7IN, NITRON, BLK, DAO, CONTRAST SIGHTS, MODULAR POLYMER GRIP, (2) 17RD STEEL MAG, RAIL”
Magazine P320 Full Size, item 320F-9-B	STEEL	—	SIG SAUER, Inc. — 2021 Guide Price List 11 8 — SIG SAUER, Inc. sigsauer.com [10] “P320, 9MM, 4.7IN, NITRON, BLK, DAO, CONTRAST SIGHTS, MODULAR POLYMER GRIP, (2) 17RD STEEL MAG, RAIL”

Function check

After every reassemblyPerform these checks on a verified-unloaded firearm. If any check fails, the firearm is not safe to fire — stop and see a licensed gunsmith.

Verify the pistol is unloaded before each check.
Rack the slide and press the trigger. The striker should release cleanly.
Hold the trigger back, rack the slide, release slowly and feel the reset.
Press the trigger again to confirm the striker releases.
If the pistol has a manual safety, confirm the trigger is blocked with the safety engaged.
Confirm the slide locks open on an empty magazine and the magazine drops free.

Maintenance

Lubrication points

Fire control unit rails where the slide rides
Barrel hood and locking lug
Outside of the barrel at the muzzle end
Rear of the barrel lug where the recoil spring assembly bears

Cleaning notes

Because the slide rides on the steel fire control unit rather than the polymer grip module, the rails are the critical lubrication point.

Suggested inspection interval: roughly every 5000 rounds. This is a general guideline, not a manufacturer specification.

Wear parts to inspect

Recoil spring assembly · Extractor · Striker and striker spring

Common issues

Symptom	Likely cause	What to do
Takedown lever will not rotate	Slide not fully locked to the rear	Lock the slide fully back before rotating the lever.
Trigger feels gritty or will not reset after swapping grip modules	Fire control unit not fully seated in the grip module	Remove and reseat the fire control unit, front first, until it sits flush.

Also covers

The procedures above are reported to apply to: SIG Sauer M17 · SIG Sauer M18 · P320 Compact · P320 X-Series · P320 XTEN. Verify against the manual for your specific model.

Similar manual of arms

Legal notes

Not legal adviceThe fire control unit is the serialized firearm. Shipping, transferring, or storing it is legally the same as doing so with a complete pistol. Swapping grip modules or slides can change the pistol's legal classification in some jurisdictions — for example, building a configuration with a shorter barrel and a stock.

Sourcing

Confidence: medium — Drawn from reliable secondary sources and consistent across references, but not confirmed against a primary source.
Verification: Community reviewed only
Last updated: 2026-10-29

References

Every source this page draws on, with its web address so you can read it yourself. Numbers in brackets elsewhere on the page point here.

[1] SIG Sauer P320 Operator's Manual — SIG Sauer, Inc. manufacturer manual primary source
[2] SIG Sauer P320 Voluntary Upgrade Program notice (2017) — SIG Sauer, Inc. (2017) manufacturer manual primary source
[3] SIG P320 Pistols Operator's Manual: Handling & Safety Instructions, 8501909-01 REV11 (Sept 2023), section 8 — SIG SAUER manufacturer manual primary source
https://www.sigsauer.com/media/sigsauer/resources/OPERATORS_MANUAL_P320_8501909-01_REV11_WEB_FILE_1.pdf (checked 2026-09-27)
[4] OPF-P320, RMR (product page) — Forward Controls Design website secondary source
https://www.forwardcontrolsdesign.com/OPF-P320-RMR_p_449.html (checked 2026-09-27)
[5] OPF-P320, RMR, RSD (product page) — Forward Controls Design website secondary source
https://www.forwardcontrolsdesign.com/OPF-P320-RMR-RSD_p_344.html (checked 2026-09-27)
[6] OPF-M17, ACRO (product page) — Forward Controls Design website secondary source
https://www.forwardcontrolsdesign.com/OPF-M17-ACRO_p_277.html (checked 2026-09-27)
[7] Adapter plate for Footprint RMR on SIG P320 Romeo 1 Pro (product page) — HOLOSUN Europe (holosun.eu, operated by Picotronic GmbH, HOLOSUN European distributor) website secondary source
https://www.holosun.eu/en/p/70189674 (checked 2026-09-27)
[8] SIG SAUER — Voluntary Upgrade Notice (P320 upgrade program customer letter) — SIG SAUER, Inc. website primary source
https://www.sigsauer.com/pub/media/sigsauer/resources/Voluntary-Upgrade-Notice-1.pdf (checked 2026-10-03)
[9] SIG SAUER, Inc. — 2019 GDS CATLOG WORKING FINAL LR — SIG SAUER, Inc. manufacturer manual primary source
https://www.sigsauer.com/pub/media/sigsauer/resources/2019_GDS_CATLOG_WORKING-FINAL-LR.pdf (checked 2026-10-03)
[10] SIG SAUER, Inc. — 2021 Guide Price List 11 8 — SIG SAUER, Inc. manufacturer manual primary source
https://www.sigsauer.com/media/sigsauer/resources/2021-Guide-Price-List-11-8.pdf (checked 2026-10-03)
[11] Trijicon RMR / SRO, Holosun 407c / 507c Mount for Sig Sauer P220, P226, P229, P320 (EGW product page, installation instructions section) — Evolution Gun Works (EGW) website secondary source
https://egwguns.com/trijicon-rmr-sro-holosun-407c-507c-mount-for-sig-sauer-p220-p226-p229-p320 (checked 2026-10-11)
[12] SIG Sauer P220 P226 P229 P320 Red Dot Mount | Fits Vortex Venom, Viper & Burris FastFire | EGW (EGW product page, installation instructions section) — Evolution Gun Works (EGW) website secondary source
https://egwguns.com/vortex-viper-venom-sig-sauer-p220-p226-p229-p320-sight-mount-fits-burris-fastfire-and-docter (checked 2026-10-11)
[13] Adapter Plate for Sig P320 (Romeo) to Vortex Venom (EGW product page, installation instructions section) — Evolution Gun Works (EGW) website secondary source
https://egwguns.com/vortex-venom-adapter-plate-for-optics-ready-sigs-cut-for-the-romeo-1-p320-rx-x-five (checked 2026-10-11)
[14] Seeking stupidity relief: P320 FCU stuck on slide. (Don't remove the takedown lever first!) - Topic — SIGforum community anecdotal source
https://sigforum.com/eve/forums/a/tpc/f/430601935/m/6910085464 (checked 2026-10-29)
[15] Building a P320 FCU from parts - Topic — SIGforum community anecdotal source
https://sigforum.com/eve/forums/a/tpc/f/430601935/m/3440076374?csra=Y&f=430601935&a=tpc&m=3440076374&s=674608412 (checked 2026-10-29)

Notes: DOWNGRADED on 2026-09-15. This entry claimed 'manufacturer-manual-verified' while citing no manual anyone could open. sigsauer.com answers every automated request from here with a 403, so the SIG P320 manual could not be read to confirm or correct the procedure. Rather than leave a verification claim that cannot be checked, the entry now says what it actually is: community-reviewed and unconfirmed against the factory manual. The procedure itself is unchanged and is believed correct, but believed is not verified.

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