PS90 SBR Guide

Convert Your FN PS90 to a Short-Barreled Rifle (SBR) – Complete ATF Compliance and Installation Guide

Looking to turn your FN PS90 into a true SBR? This detailed guide walks you through the entire PS90 SBR conversion process—from ATF Form 1 approval and NFA engraving requirements to safe barrel removal and proper installation of a 10.4" barrel. Restore the compact proportions of the original P90 platform while staying fully compliant with federal law.

Legal Disclaimer:
This guide is provided for informational purposes only and does not constitute legal advice. Always consult with a qualified NFA attorney to ensure compliance with all applicable federal, state, and local firearms laws before modifying any firearm.

Compliance Overview

To legally convert your FN PS90 to a short-barreled rifle (SBR) under the National Firearms Act (NFA), you must:

  • Submit ATF Form 1, pay the $200 tax stamp, and wait for approval before completing any modifications
  • Ensure the firearm is engraved with your name/trust name, city, and state as per ATF guidelines

Important: Possessing or assembling an SBR before receiving Form 1 approval is a federal crime.

Submitting ATF Form 1 for a PS90 SBR

Apply online at eForms.atf.gov. You’ll need the following:

  • An eForms account
  • A completed ATF Form 1
  • Passport-style photo and fingerprint submission
  • $200 tax stamp fee

Note: As of now, the $200 tax stamp fee is scheduled to be eliminated starting January 1 under the One Big Beautiful Bill (OBBB). Be sure to verify the most current regulations before applying.

How to Fill Out ATF Form 1 for a PS90 SBR

Use the following entries when completing the firearm description portion of your ATF Form 1:

  • Section 4(a): Name and Address of Original Manufacturer and/or Importer of Firearm (If any): FN Herstal
  • Section 4(b): Type of Firearm to be made: Short-Barreled Rifle (SBR)
  • Section 4(c): Caliber: 5.7x28mm
  • Section 4(d): Model: PS90
  • Section 4(e): Barrel Length: 10.4"
  • Section 4(f): Overall Length: 20.0" (may vary slightly depending on muzzle device)
  • Section 4(g): Serial Number: Enter the existing serial number of your PS90 exactly as marked
  • Section 4(h): FN PS90 converted to SBR with aftermarket 10.4" barrel and OEM-spec retention system
  • Section 4(i): For all lawful purposes, including personal collection and sporting use

Be sure to measure the firearm in its completed SBR configuration before submitting dimensions.

Engraving Requirements

Once your Form 1 is approved, you must engrave the following information on your PS90:

  • Name (or trust name), city, and state as shown in Section 3B of your Form 1
  • Minimum depth: 0.003"
  • Minimum character height: 1/16"
  • Engraving must be placed in a visible location on the receiver

Removing the Factory Barrel and Shroud

There are two methods for removing the factory 16″ barrel and shroud from your PS90. The preferred and safest approach is using the Dorin Technologies PS90 Barrel Shroud Removal Jig System. A manual alternate method is also outlined below for users without the jig system.

Preferred Method: Dorin Technologies Jig System

We recommend the Dorin Technologies PS90 Barrel Shroud Removal Jig System for precise, repeatable, and safe barrel and shroud removal.

Follow the video instructions included with the jig system for complete guidance. Here's an overview:

  • Secure the receiver horizontally in a non-marring vise.
  • Install the printed drill alignment tool into the receiver to align the bit to the proper location on the shroud.
  • Drill the pin access hole using the included 5/64″ drill bit.
  • Remove the receiver from the vise and install the aluminum jig into the vise.
  • Insert the stainless steel muzzle plate into the flash hider to protect the muzzle.
  • Using a 15 mm crowfoot or thin wrench on the barrel’s breech end, loosen the barrel (left-hand threads).
  • Drift out the factory blind pin with a 1/16″ punch and use compressed air to remove debris.
  • Slide off the shroud, leaving the barrel installed in the receiver.
  • Insert a .22-caliber cleaning rod through the front of the receiver to retain internal components.
  • Pull the 16″ barrel out through the rear while holding the cleaning rod steady. This preserves the return spring and simplifies reassembly.

Alternate Method (Without the Dorin Technologies Jig System)

If the jig system is not available, you can manually drill and remove the blind pin using the following steps. For a visual walkthrough, watch the YouTube tutorial here.

Step 1: Drill the Hole & Remove the Blind Pin

  • Use a Sharpie to mark two dots 5/8″ apart on masking tape.
  • Place a punch through one dot and align it with the existing blind pin hole on the underside of the shroud.
  • Apply the tape to the shroud so the second dot is underneath the shroud wall where the new hole will be drilled.
  • Use a marking punch to make a small dimple at the second dot.
  • With a 5/64″ drill bit in a handheld drill, start perpendicular to the shroud, then gradually angle the bit toward the blind pin.
  • Use a 1/8″ drift punch and hammer to tap the blind pin out through the new hole.
  • Blow compressed air into the new hole to remove debris and metal shavings that could affect barrel thread integrity.

Step 2: Remove the Shroud & Retain Internal Components

  • Insert a 2″ × 1¼″ × ⅛″ metal plate into the flash hider and secure the muzzle in a non-marring vise.
  • Using a 15 mm thin wrench or crowfoot wrench, loosen the barrel from the breech end. Note: These are left-hand threads, so turn clockwise to loosen.
  • Slide the shroud forward off the barrel, leaving the barrel installed in the receiver.
  • Insert a .22-caliber cleaning rod (at least 20″ long) through the front of the receiver to retain the return spring and internal components.
  • While holding the rod steady, slide the 16″ barrel out through the rear of the receiver.

Why You Should Avoid Cutting the Factory 16″ Barrel

  • Factory 16″ barrels are not available from FN or authorized distributors, are rarely found on the aftermarket, and once you cut it, obtaining a replacement is extremely difficult.
  • Many users regret cutting the factory barrel—often not immediately, but almost always later when replacement parts are needed or resale is considered.
  • Improper cuts can affect reliability or safety due to the PS90’s floating barrel design and delayed blowback system.

Recommendation: Use a dedicated short barrel like the CMMG 10.4″ PS90 barrel and keep your original barrel intact for future restoration or resale.

Installing the 10.4" Barrel

  • Ensure the internal components are still properly seated.
  • Slide the new barrel in from the rear of the receiver, over the .22 cleaning rod that should still be in place.
  • Carefully jimmy the barrel through the internal components until it seats into position.
    Then, remove the .22 cleaning rod from the front of the barrel.
  • Ensure the barrel return spring is still in place.
  • Install your desired muzzle device on the muzzle end.
  • Align the barrel so the muzzle device mount is properly oriented.
  • Use a 15mm crowfoot or thin wrench to snug the barrel into place. Do not overtighten.
    Note: the barrel uses left-hand threads.
    For professional installation, torque to 40–50 Nm (29.5–36.9 ft-lbs), as specified in the FN P90 Armorer’s Manual.
  • Confirm the barrel is securely installed but free-floating inside the receiver to preserve the PS90’s delayed blowback operation.
    The barrel should have slight rotational and front-to-back play once properly seated.

Final Reassembly and Function Check

  • Reinstall the upper receiver assembly onto the PS90’s stock.
  • Verify that the charging handle, bolt, and barrel move freely.
  • Perform a function check to confirm proper cycling.
  • Confirm that the barrel has slight play (rotational and front-to-back), ensuring proper operation of the PS90’s floating barrel system.
  • Do not proceed to live-fire testing until the firearm has passed a full manual function check.

Frequently Asked Questions (FAQs)

Can I convert the same PS90 back and forth between a rifle and an SBR?

Yes. Once your PS90 is lawfully registered as a short-barreled rifle (SBR) via ATF Form 1, you may configure and reconfigure it between SBR and rifle setups. For example, you can reinstall the 16" barrel to return it to rifle length, and later switch back to a short barrel. However, it remains an NFA-regulated firearm until formally removed from the registry.

Can I remove it from the NFA registry later?

Yes. To declassify the firearm and remove it from the National Firearms Act (NFA) registry, you must submit a written request to the ATF. This typically includes confirmation that the short barrel has been removed and the firearm is no longer configured as an SBR—often supported with photographs or other evidence. Once the ATF processes and confirms the removal, the firearm is no longer regulated as an NFA item.

What happens if I install the barrel before Form 1 approval?

Installing a barrel shorter than 16" on a rifle before Form 1 approval is a federal offense. The SBR must not exist until the approved Form 1 is in hand and your tax stamp is issued.

Do I need to engrave if the firearm is already marked by FN?

Yes. Even though the firearm has factory markings from FN, you must add your own information (name/trust, city, state) per ATF Form 1 requirements. This marking must be permanent, legible, and meet the minimum depth and height standards set by the ATF.

Can I use a trust to register my SBR?

Yes. Many people use a gun trust to register NFA items. Make sure your trust is properly set up and includes all responsible persons. Everyone listed must submit fingerprint cards and photos with the Form 1 application.

Can I sell the SBR later?

Yes, but it requires a proper NFA transfer (Form 4) to another individual, dealer, or SOT holder. However, it is often much easier to remove the short barrel, re-install the factory 16" barrel and shroud, and submit a declassification request to the ATF. Once approved, the firearm is no longer an NFA item and can be sold or transferred like a standard Title I firearm.

Legal Disclaimer

This guide is provided for informational and educational purposes only. It does not constitute legal advice or replace consultation with a qualified firearms attorney. Federal, state, and local laws are subject to change, and interpretations may vary. Always verify current regulations before modifying any firearm or submitting paperwork to the ATF.

Possessing, assembling, or modifying an NFA-regulated item without proper authorization is a serious federal offense. FN Specialties, Dorin Technologies, and all related entities are not responsible for misuse of this information or non-compliance with applicable laws.

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