FN SCAR 17S

easy
Shop tier 2
medium confidence
Rifle
short stroke piston
battle rifle
folding stock
quick change barrel
reciprocating handle

field strip ~2 min · reassembly ~4 min · detail strip ~30 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.

FN Herstal limits owner disassembly The maker's own procedure goes as far as: Trigger module, buttstock module, moving parts (bolt carrier, charging sled, bolt removed from carrier), gas regulator and piston. Do not disassemble the bolt, the buffer or the charging sled further.. FN tells owners not to take the action apart beyond the manual's procedure (no bolt or buffer disassembly) and to contact the FN Service Center if further disassembly is needed. (FN SCAR 16S/17S/20S Owner's Manual (2512) — FN America, LLC, p. 42 fnamerica.com [7])

Specifications

Manufacturer: FN Herstal
Origin: Belgium / United States
Category: Rifle
Action: Gas, short-stroke piston
Calibers: 7.62x51mm NATO, .308 Winchester, 5.56x45mm NATO
Capacity: 20+1 in 7.62mm
Production: 2009–present (in-production)
Also known as: SCAR-H, Mk 17, SCAR 16S (5.56 version)

Model-specific safety

The SCAR uses a short-stroke piston and a monolithic aluminium upper receiver. The reciprocating charging handle moves with the bolt during firing — keep your support hand clear of its path.
The barrel is retained by bolts through the upper receiver and is user-changeable, but that is a torque-specified operation affecting headspace. Follow the manufacturer’s procedure.
The gas regulator has normal and suppressed settings. The wrong setting either batters the rifle or stops it cycling.
The folding stock must be locked in the extended position for normal shooting. Confirm the lock.
Gas system components are extremely hot after firing.

Under spring tension

Recoil springs on the guide rods
Gas piston spring
Magazine spring

Easily lost parts

Bolt cam pin · Firing pin retaining pin · Gas piston and regulator

Tools

No tools required for the field strip.

Shop difficulty

Shop tier 2 Tier 2 — moderate among rifles and carbines, for the full job: strip to the parts that get coated and put it back together working. The upper is a monolithic receiver; the barrel comes out on six captive Torx screws torqued in sequence, and the trigger module, bolt carrier and stock come off with finger pressure. FN treats the trigger module and other inner assemblies as factory-only, and a barrel removal means a headspace check. There are few parts to handle, but the torque spec, headspace gauging and a sealed trigger module make it moderate.

No sourced part count yet.

Bench time: about 40 min to strip, 60 min to rebuild (estimate). Estimate: field strip (trigger module, return spring, bolt carrier, charging handle), barrel out on six screws, front/rear sights, muzzle device, stock and hinge, lower; trigger module not stripped. Rebuild longer for the barrel screw torque sequence, headspace check and function check.

What comes off for coating

Upper receiver: barrel assembly (6 captive T-25 screws), charging handle, bolt carrier and bolt (firing pin, cam pin, extractor), return spring assembly, front and rear folding sights, flash hider — T-25 Torx, in-lb torque wrench, headspace gauges
Lower / trigger module: trigger module (removed as a unit, not stripped), lower receiver
Stock: folding stock assembly and hinge, cheek piece, butt plate

Special tools

Inch-pound torque wrench with T-25 Torx bit — Barrel screws, 62 in-lb (7 N·m)
GO/NO-GO headspace gauges (7.62x51) — After the barrel is refitted
M16/AR15 A2 front sight tool — Front sight post
Muzzle device wrench — Flash hider

Known pain points

FN says the inner mechanism assemblies (trigger module internals, bolt) are finely fitted and go back to FN for anything past the field strip. (both)
Source: Autoloading Rifle Owner's Manual FN SCAR 16S and 17S (2016) — FN America s3.amazonaws.com [9] — “YOU MAY DAMAGE IT BEYOND REPAIR OR LOSE SMALL PARTS BY ATTEMPTING TO DISASSEMBLE THE INNER MECHANISM ASSEMBLIES.”
The six barrel screws are captive: they are backed to the end of travel but not removed, then torqued back in a rear-to-front alternating sequence at 62 in-lb; a ft-lb wrench strips them. (both)
Source: Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC fnamerica.com [4] — “Using the torque wrench set at 62 inch-pounds (7Nm) and a TORX T-25 adapter, tighten the barrel screws starting at the rear of the barrel extension (alternating sides)”
Any barrel off/on needs a GO/NO-GO headspace check by an armorer. (reassembly)
Source: Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC fnamerica.com [4] — “the headspace must be checked by a certified armorer or gunsmith using a set of GO/NO-GO headspace gages”

Fit or check on rebuild

Barrel screw torque and sequence — Rear-to-front, alternating, 62 in-lb
Source: Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC fnamerica.com [4] — “Using the torque wrench set at 62 inch-pounds (7Nm) and a TORX T-25 adapter, tighten the barrel screws starting at the rear of the barrel extension (alternating sides)”
Headspace — Bolt/barrel combination must be gauged after a barrel change
Source: Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC fnamerica.com [4] — “the headspace must be checked by a certified armorer or gunsmith using a set of GO/NO-GO headspace gages”
Zero — The barrel moves relative to the top rail and optics; re-zero

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

Procedures

Clear and Make Safe

Clear & Make Safe

Point the muzzle in a safe direction and keep your finger off the trigger.
Place the selector on safe.
Press the magazine release and remove the magazine.
Removed at this step: Magazine
Pull the charging handle fully to the rear and lock the bolt back if the rifle has a hold-open.
Inspect the chamber and magazine well with a light, then physically confirm the chamber is empty.
WarningLook and feel. Both, every time.
Remove all live ammunition from the work area.

Field Strip

Complete the Clear and Make Safe procedure and release the bolt forward.
Push out the two receiver takedown pins.
Removed at this step: Takedown pins
Separate the upper receiver from the lower receiver.
Removed at this step: Upper receiver assembly
Withdraw the bolt carrier group and its recoil spring guide rods rearward out of the upper receiver.
WarningThe recoil springs are under compression.
Removed at this step: Bolt carrier group Recoil spring assembly
Remove the firing pin retaining pin, withdraw the firing pin, rotate and lift the cam pin, and withdraw the bolt.
Removed at this step: Firing pin Cam pin Bolt
Rotate and withdraw the gas piston and its components from the gas block, noting orientation.
Removed at this step: Gas piston

Reassembly

Reinstall the gas piston and its components in the correct orientation.
Fit the bolt into the carrier, install and rotate the cam pin, then the firing pin and retaining pin.
Insert the bolt carrier group and guide rods into the upper receiver and seat them.
Mate the upper to the lower and press both takedown pins fully home.
Cycle the action several times 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
Barrel screws: four rear barrel extension screws and two forward barrel support screws (captive, TORX T-25) FN SCAR 16S and 17S	62 in-lb 7 N·m · 5.2 ft-lb	Seat the barrel extension lugs in the receiver cutaway, slide rearward until all barrel extension screws align, guide the front barrel support into the receiver; tighten the barrel screws starting at the rear of the barrel extension (alternating sides) and moving forward, per the 1-6 sequence in Figure 11, applying downward pressure. “Using the torque wrench set at 62 inch-pounds (7Nm) and a TORX T-25 adapter, tighten the barrel screws starting at the rear of the barrel extension (alternating sides) and moving forward on the rifle (Figure 11).”	Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC, PDF p. 2 (Barrel Assembly Installation, fnamerica.com [4]
Barrel extension screws (TORX T-25), refitting the barrel after NRCH conversion FN SCAR 16S/17S (NRCH kit P/N 20-100505 for 17S/20S)	62 in-lb 7 N·m · 5.2 ft-lb	Starting from the rear, in the order of Figure 18 (1-6), applying downward pressure and turning clockwise. “Using the torque wrench set at 62 inch-pounds (7Nm) and a TORX® T-25 adapter, starting from the rear, tighten the barrel extension screws in the order outlined in Figure 18.”	Instructions for FN SCAR Non-Reciprocating Charging Handle Kit (FN002 R3) — FN America, LLC, PDF p. 12 fnamerica.com [5]
NRCH front plate screws (2.5 mm hex) FN SCAR 16S/17S converted with FN's NRCH kit (P/N 20-100505 for 17S/20S)	22.1 in-lb 2.5 N·m · 1.8 ft-lb	Threadlocker: Loctite 263 permanent high strength thread locker (or equivalent); allow 24 hours cure “Use a torque wrench set at 22.1 in/lbs (2.5Nm) with a 2.5mm hex bit to tighten the two front plate screws.”	Instructions for FN SCAR Non-Reciprocating Charging Handle Kit (FN002 R3) — FN America, LLC, PDF p. 10 fnamerica.com [5]
SCAR-SC receiver rear plate screws (four 2.5 mm side screws, one 3 mm top screw) FN SCAR 16S/17S/20S fitted with FN's SCAR-SC rear stock ("installation procedures for SCAR 16S, SCAR 17S and SCAR 20S are identical")	22.1 in-lb 2.5 N·m · 1.8 ft-lb	Threadlocker: Loctite 263 permanent high strength thread locker (or equivalent); allow 24 hours cure “Use a torque wrench set at 22.1 in/lbs (2.5Nm) with a 2.5mm hex bit to tighten the four side screws and a 3mm hex bit for the top screw.”	Instructions for FN SCAR-SC Rear Stock (2407) — FN America, LLC, PDF p. 2 fnamerica.com [6]
M-LOK QD sling mount screws (5/32" hex) FN SCAR 16S, 17S, 20S	max. 35 in-lb 4 N·m · 2.9 ft-lb	“Secure the M-LOK screws using a 5/32” hex wrench (Do not exceed 35 in/lbs.).”	FN SCAR 16S/17S/20S Owner's Manual (2512) — FN America, LLC, PDF p. 57 (M-LOK QD sling mount) fnamerica.com [7]
M-LOK vertical foregrip screws (5/32" hex) FN SCAR 16S and 17S	max. 15 in-lb 1.7 N·m · 1.2 ft-lb	“Secure the M-LOK screws using a 5/32” hex wrench (Do not exceed 15 in/lbs.).”	FN SCAR 16S/17S/20S Owner's Manual (2512) — FN America, LLC, PDF p. 58 (22.4 Vertical foregrip) fnamerica.com [7]

Notes: The manufacturer's documents give no torque value. They say: "Reinsert the safety selector lever screw into the larger hole of the safety selector lever and hand-tighten with a 5/64” flathead screwdriver until the screw is flush with the safety selector lever body (Figure 69). Do not over tighten." (FN SCAR 16S/17S/20S Owner's Manual (2512), PDF p. 55) "Install the rear sight assembly to the receiver top rail using a T25 wrench. Use only enough torque to snug the clamping screw." (Instructions for FN SCAR-SC Rear Stock (2407), PDF p. 2)

Reported by other sources — not the manufacturer

Not a manufacturer specificationThese values come from the people and publications named beside each one, not from FN Herstal, 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
Rear barrel extension screws (4, T-25 Torx) FN SCAR 16 and 17 (instructions for fitting the Midwest Industries MI-S1617 extension rail, which reuses the factory screws)	62 in-lb 7 N·m · 5.2 ft-lb	Reported by Midwest Industries, Inc. Secondary — a parts or tool maker, or a gunsmithing publisher Start the forward barrel screws (do not tighten), slide the barrel rearward and start the 4 rear barrel extension screws (do not tighten), fit the rail, then tighten the four rear barrel extension screws in an alternating pattern; then the six remaining T-25 screws in the rail and front trunnion to 45 in/lbs. 'DO NOT attempt to remove the receiver assembly screws, located in the middle of each block.' “Tighten the four rear barrel extension screws in an alternating pattern to 62 in/lbs. of torque.”	MI-S1617 FNH SCAR 16, 17 Extension Rail Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [2]
Barrel screws (factory four T25 screws) FN SCAR (barrel assembly to upper receiver; KDG MREX MkII rail instructions)	62 in-lb 7 N·m · 5.2 ft-lb	Reported by Kinetic Development Group (KDG) Secondary — a parts or tool maker, or a gunsmithing publisher Slide the barrel (with rail) assembly into the upper receiver and tighten the factory four T25 screws in a crisscross pattern. “FNH recommends tightening the barrel to the factory installed 62 in/lbs in a crisscross pattern.”	MREX MkII Installation Instructions — Kinetic Development Group (KDG) kineticdg.com [3]
Rail and front trunnion screws (6, T-25), with MI extension rail fitted FN SCAR 16/17 fitted with Midwest Industries MI-S1617 extension rail	45 in-lb 5.1 N·m · 3.7 ft-lb	Reported by Midwest Industries, Inc. Secondary — a parts or tool maker, or a gunsmithing publisher “Tighten the six remaining T-25 screws in the rail and front trunion to 45in/lbs.”	MI-S1617 FNH SCAR 16, 17 Extension Rail Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [2]

Fastener

Torque

Who says so, and their words

Where it comes from

Rear barrel extension screws (4, T-25 Torx)
FN SCAR 16 and 17 (instructions for fitting the Midwest Industries MI-S1617 extension rail, which reuses the factory screws)

62 in-lb
7 N·m · 5.2 ft-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Start the forward barrel screws (do not tighten), slide the barrel rearward and start the 4 rear barrel extension screws (do not tighten), fit the rail, then tighten the four rear barrel extension screws in an alternating pattern; then the six remaining T-25 screws in the rail and front trunnion to 45 in/lbs. 'DO NOT attempt to remove the receiver assembly screws, located in the middle of each block.'

“Tighten the four rear barrel extension screws in an alternating pattern to 62 in/lbs. of torque.”

MI-S1617 FNH SCAR 16, 17 Extension Rail Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [2]

Barrel screws (factory four T25 screws)
FN SCAR (barrel assembly to upper receiver; KDG MREX MkII rail instructions)

62 in-lb
7 N·m · 5.2 ft-lb

Reported by Kinetic Development Group (KDG)
Secondary — a parts or tool maker, or a gunsmithing publisher

Slide the barrel (with rail) assembly into the upper receiver and tighten the factory four T25 screws in a crisscross pattern.

“FNH recommends tightening the barrel to the factory installed 62 in/lbs in a crisscross pattern.”

MREX MkII Installation Instructions — Kinetic Development Group (KDG) kineticdg.com [3]

Rail and front trunnion screws (6, T-25), with MI extension rail fitted
FN SCAR 16/17 fitted with Midwest Industries MI-S1617 extension rail

45 in-lb
5.1 N·m · 3.7 ft-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

“Tighten the six remaining T-25 screws in the rail and front trunion to 45in/lbs.”

MI-S1617 FNH SCAR 16, 17 Extension Rail Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [2]

Materials and factory finish

As stated by FN Herstal. 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
Receiver (upper) FN SCAR 17S NRCH, 16.25in (page lists BLK, FDE and GRY colour SKUs)	aluminum	Hard-anodized	FN SCAR® 17S NRCH — product page (Specs / Primary Features) — FN America, LLC fnamerica.com [8] “RECEIVER … Hard-anodized monolithic aluminum”
Barrel FN SCAR 17S NRCH, 16.25in (page lists BLK, FDE and GRY colour SKUs)	—	chrome-lined	FN SCAR® 17S NRCH — product page (Specs / Primary Features) — FN America, LLC fnamerica.com [8] “BARREL … Cold hammer-forged, chrome-lined, fully free-floating with compensator”
Stock FN SCAR 17S NRCH, 16.25in (page lists BLK, FDE and GRY colour SKUs)	polymer	—	FN SCAR® 17S NRCH — product page (Specs / Primary Features) — FN America, LLC fnamerica.com [8] “STOCK … Telescoping side-folding polymer stock”
Magazine FN SCAR 17S NRCH, 16.25in (page lists BLK, FDE and GRY colour SKUs)	Steel	—	FN SCAR® 17S NRCH — product page (Specs / Primary Features) — FN America, LLC fnamerica.com [8] “MAGAZINE … Steel body”

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 rifle is unloaded with no magazine inserted before each step.
Cycle the action by hand and confirm the bolt locks and returns fully to battery.
With the selector on safe, press the trigger. The hammer must not fall.
Move the selector to fire, cycle the action, and press the trigger. The hammer should fall.
Hold the trigger back, cycle the action, and release slowly to feel the disconnector reset.
Confirm the magazine seats and locks positively and any hold-open engages on an empty magazine.
Confirm the folding stock locks positively in the extended position.
Confirm the gas regulator is on the correct setting.

Maintenance

Lubrication points

Bolt lugs and body
Cam pin or cam track
Carrier rails
Gas piston (a light film only)
Hammer and sear pivots

Cleaning notes

A short-stroke piston keeps most combustion fouling out of the receiver, which is the point of the system — but the piston, its cylinder, and the gas block still need periodic cleaning. Do not scrub the piston bright; a light carbon film is normal.

Suggested inspection interval: roughly every 1000 rounds. This is a general guideline, not a manufacturer specification.

Wear parts to inspect

Gas piston and rings · Bolt lugs · Extractor and spring · Recoil spring

Common issues

Symptom	Likely cause	What to do
Charging handle striking the support hand	The SCAR charging handle reciprocates	Adjust hand position. The handle can be swapped to the other side on most models.
Rifle short-strokes	Gas regulator setting or a fouled piston	Check the regulator, then clean the piston and gas block.

Also covers

The procedures above are reported to apply to: FN SCAR 16S in 5.56mm · Mk 16 and Mk 17 military variants. Verify against the manual for your specific model.

Similar manual of arms

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] FN SCAR 17S Operator’s Manual — FN America manufacturer manual primary source
[2] MI-S1617 FNH SCAR 16, 17 Extension Rail Installation Instructions — Midwest Industries, Inc. manufacturer manual secondary source
https://midwestindustriesinc.com/content/installation-instructions/SCAR-Extension-Rail-MI-S1617-Instructions.pdf (checked 2026-09-27)
[3] MREX MkII Installation Instructions — Kinetic Development Group (KDG) website secondary source
https://kineticdg.com/instruction/mrex-mkii-installation-instructions/ (checked 2026-09-27)
[4] Instructions for FN SCAR 16S and 17S Barrel Change (63903, 2303) — FN America, LLC manufacturer manual primary source
https://fnamerica.com/wp-content/uploads/2024/08/SCAR-Carbine-Accessory-Barrel-Instructions_63903_2303-1.pdf (checked 2026-09-27)
[5] Instructions for FN SCAR Non-Reciprocating Charging Handle Kit (FN002 R3) — FN America, LLC manufacturer manual primary source
https://fnamerica.com/wp-content/uploads/2024/02/FN002-SCAR-NRCH-Instruction-Manual-R3-05-20-2269.pdf (checked 2026-09-27)
[6] Instructions for FN SCAR-SC Rear Stock (2407) — FN America, LLC manufacturer manual primary source
https://fnamerica.com/wp-content/uploads/2025/02/2407_FNSCAR-SC-Stock-Install.pdf (checked 2026-09-27)
[7] FN SCAR 16S/17S/20S Owner's Manual (2512) — FN America, LLC manufacturer manual primary source
https://fnamerica.com/wp-content/uploads/2026/01/2512_FNSCAR_16S17S20S_OM_.pdf (checked 2026-09-27)
[8] FN SCAR® 17S NRCH — product page (Specs / Primary Features) — FN America, LLC website primary source
https://fnamerica.com/products/rifles/fn-scar-17s-nrch/ (checked 2026-10-03)
[9] Autoloading Rifle Owner's Manual FN SCAR 16S and 17S (2016) — FN America manufacturer manual primary source
https://s3.amazonaws.com/files.ammunitiondepot.com/fn-firearms/carbines-discontinued/fn-scar-16s-17s-owners-manual-2016.pdf (checked 2026-10-29)

Notes: Rated medium pending step-by-step confirmation against the factory manual. The reciprocating charging handle and the gas regulator settings are the two things most likely to matter in practice.

Found something wrong? Corrections are the most valuable contribution to this project. Open an issue with the model, the step, and a source.