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FN PS90

• easy
• Shop tier 3
• high confidence
• Carbine
• bullpup
• blowback
• polymer frame
• top mounted magazine

field strip ~2 min · reassembly ~3 min

Specifications

Model-specific safety

• The moving parts group and the hammer group come out only with the hammer cocked. Once the moving parts group is out, do not pull the trigger: the hammer drops to its decocked position and the hammer group can no longer be removed. If that happens, reassemble, cock the carbine with the cocking handle and start again.
• When the magazine is on the carbine, the last two cartridges and the cartridge in the chamber are not visible. Always remove the magazine and look into the chamber through the magazine opening.
• FN states that removal of metal from the barrel, or modification of the firing mechanism or operating parts, may lead FN to refuse service, and that FN will charge for parts and labour to return the firearm to original specification. Threading or cutting the barrel is exactly this kind of work.
• FN specifies specially coated factory-loaded 5.7x28mm ammunition only, and says non-factory ammunition can produce pressures that injure the shooter and damage the firearm.

Under spring tension

• Magazine follower spring (bears on the magazine bottom lock during magazine disassembly)

Easily lost parts

Magazine rollers (2)

Tools

No tools required for the field strip.

Shop difficulty

Shop tier 3 Tier 3 — hardest among rifles and carbines, for the full job: strip to the parts that get coated and put it back together working. Mostly polymer, with a field strip into four groups that takes seconds. Past that, the hammer group and frame/trigger group are polymer assemblies held by pins and springs, and FN restricts them to its service centre or an armorer. The hammer group has to be in a particular state when it comes apart. With no published parts list and armorer-only internals, it sits with the hardest rifles here on uncertainty as much as evidence.

No sourced part count yet.

Bench time: about 50 min to strip, 80 min to rebuild (estimate). Estimate: field strip into four groups, then the hammer group, frame/trigger group, barrel support/rail, butt plate and magazine catch. Rebuild longer: polymer internals with pins and springs, and the function check. High uncertainty.

What comes off for coating

• Barrel support and upper rail group: barrel and support, upper rail, sights
• Frame and trigger group: trigger system, fire selector, magazine catch, ejection chute — pin punches
• Moving parts group: breech block, guide rods and return springs
• Hammer group: hammer group (polymer, pins and springs) — pin punches
• Butt plate: butt plate

Special tools

• Pin punches (polymer-safe) — Hammer and trigger group pins
• Sight adjustment tool — Rail sight

Known pain points

• FN limits the owner to the four-group field strip; anything further (hammer group, trigger group, barrel support) is service-centre/armorer work. (both)
  Source: FN PS90 Autoloading Carbine Owner's Manual (1605, OM 3810054200) — FN America, LLC fnamerica.wpenginepowered.com [1] — “further disassembly should only be carried out by a FN Recommended Service Center / your departmental armorer.”
• The hammer must be cocked (raised) before the hammer group comes out; if the trigger has been pulled with the moving parts out, the carbine has to be reassembled and re-cocked first. (both)
  Source: FN PS90 Autoloading Carbine Owner's Manual (1605, OM 3810054200) — FN America, LLC fnamerica.wpenginepowered.com [1] — “If the trigger has been pulled after the removal of the moving parts, reassemble the carbine, cock the hammer by pulling the cocking handle completely rearward and then start disassembling again.”
• The hammer group is a polymer assembly held together by pins and springs; owners advise leaving it to a gunsmith who knows the PS90. (both)
  Owners report: FN PS90 review/thread — Canadian Gun Nutz canadiangunnutz.com [2] — “Unless you are a gunsmith familiar with the PS90 I would not suggest getting your punches and pliers out and stripping the gun any further.”

Fit or check on rebuild

• Hammer group dry — FN: hammer group components are never lubricated
  Source: FN PS90 Autoloading Carbine Owner's Manual (1605, OM 3810054200) — FN America, LLC fnamerica.wpenginepowered.com [1] — “Components of the hammer group may never be lubricated”
• Function check — Safety, internal safety sear and trigger reset after the hammer group goes back
• Zero — Optic/sight on the barrel support must be re-zeroed

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

Procedures

Torque specifications

No sourced torque values from the manufacturer are recorded for this firearm. Where a fastener has a specified torque — action screws, scope bases, muzzle devices, barrel nuts — get it from the manufacturer or a gunsmith rather than estimating it.

What the manufacturer does say: FN's owner's manual gives no torque values.

Function check

• Every group locks into position on reassembly; none can be pulled out without its lock or release lever.
• With an empty magazine fitted and the chamber empty, the hammer falls when the trigger is pulled.
• If the carbine does not fire or function, check that the fire selector is not on 'S', that it has been cocked, and that it has been reassembled correctly — FN's own troubleshooting order.

Maintenance

Cleaning notes

FN asks that the carbine be cleaned before it is first fired. It also asks for an inspection every 10,000 rounds or once a year by an FN Recommended Service Center, because wear and corrosion are not always visible from the outside.

Similar manual of arms

• FN Five-seveN

Legal notes

Sourcing