Threaded barrels are legal to own as standalone parts in Washington State. The problem starts when you attach one to the wrong firearm. Under Washington’s 2023 assault weapon ban, a single threaded barrel on a semi-automatic center-fire rifle or pistol with a detachable magazine can reclassify that firearm as a prohibited “assault weapon,” making it illegal to manufacture, sell, or import within the state. Whether your setup crosses that line depends on the firearm’s action, its chambering, and how it feeds.
When a Threaded Barrel Turns a Firearm Into an Assault Weapon
Washington uses a feature-based test. The law doesn’t ban threaded barrels themselves. It defines “assault weapon” partly by listing physical characteristics that, when present on qualifying semi-automatic firearms, trigger the classification.
For a semi-automatic, center-fire rifle with a detachable magazine, one listed feature is enough. A threaded barrel designed to accept a flash suppressor, sound suppressor, muzzle brake, or similar device is on that list. So are folding or telescoping stocks, pistol grips, forward grips, flash suppressors, and muzzle brakes.1Washington State Legislature. Washington Code 9.41.010 – Definitions The “one or more” standard is stricter than some other states that require two features. A single threaded barrel on an otherwise ordinary AR-platform rifle with a detachable magazine is enough by itself.
Semi-automatic pistols with detachable magazines face the same one-feature test. A threaded barrel capable of accepting a flash suppressor, forward handgrip, or silencer qualifies the pistol as an assault weapon. Other listed pistol features include a second handgrip, a barrel shroud, and the ability to accept a magazine outside the pistol grip.1Washington State Legislature. Washington Code 9.41.010 – Definitions
Firearms the Rule Doesn’t Reach
The feature test has real gaps. If your firearm falls into one of these categories, a threaded barrel doesn’t trigger the ban.
Rimfire rifles are outside the definition. The statute targets “semiautomatic, center fire” rifles specifically, so a threaded 10/22 in .22 LR isn’t covered no matter what features it carries.1Washington State Legislature. Washington Code 9.41.010 – Definitions
Semi-automatic shotguns can be classified as assault weapons in Washington, but the shotgun feature list doesn’t include threaded barrels. It’s limited to folding or telescoping stocks, pistol grips, thumbhole stocks, forward grips, fixed magazines over seven rounds, and revolving cylinders.2Washington State Legislature. RCW 9.41.010 – Definitions A threaded barrel on a semi-auto shotgun doesn’t, on its own, cause a problem.
Manually operated firearms are explicitly excluded. Bolt-action, pump-action, lever-action, and slide-action firearms fall outside the assault weapon definition regardless of features.2Washington State Legislature. RCW 9.41.010 – Definitions A bolt-action precision rifle with a threaded muzzle is fine.
Fixed-magazine center-fire rifles are also outside the rifle feature test, which applies only to rifles that accept a detachable magazine. A semi-automatic center-fire rifle with a permanently fixed magazine of ten rounds or fewer isn’t classified as an assault weapon based on a threaded barrel alone. Watch the magazine capacity, though: a fixed magazine holding more than ten rounds independently qualifies the rifle as an assault weapon, features aside.1Washington State Legislature. Washington Code 9.41.010 – Definitions
What the Ban Actually Prohibits
The assault weapon ban, codified as RCW 9.41.390 and enacted through HB 1240 in April 2023, doesn’t ban possession. It bans manufacturing, importing, distributing, selling, and offering for sale assault weapons within the state.3Washington State Legislature. RCW 9.41.390 – Assault Weapons Manufacturing, Importing, Distributing, Selling Prohibited That distinction shapes almost every practical question.
If you legally owned a firearm that met the assault weapon definition before April 25, 2023, you can keep it. The legislature said its intent was to “limit the prospective sale of assault weapons, while allowing existing legal owners to retain the assault weapons they currently own.”3Washington State Legislature. RCW 9.41.390 – Assault Weapons Manufacturing, Importing, Distributing, Selling Prohibited You just can’t sell or transfer it in Washington except through narrow channels: to a licensed dealer, to a licensed gunsmith for service or repair, or to law enforcement.
The real legal risk from threaded barrels is in post-ban modifications. The statute defines “manufacture” broadly to include fabrication, making, formation, production, or construction of a firearm.4State of Washington. House Bill 1240 Take a semi-automatic center-fire rifle with a detachable magazine that currently has no listed features, install a threaded barrel on it, and you have arguably manufactured a new assault weapon. That is illegal under RCW 9.41.390. The definition also reaches conversion kits and parts combinations: parts from which a firearm can be converted into an assault weapon, when kept under the same person’s control as the firearm, can themselves be classified as an assault weapon.1Washington State Legislature. Washington Code 9.41.010 – Definitions
Adding a threaded barrel to a firearm that already qualified as an assault weapon before the ban is different. You’re modifying one you already lawfully possess rather than creating a new one. The ban targets the creation of new assault weapons, not alterations to grandfathered ones.
One trap to notice: swapping a threaded barrel for a plain one doesn’t always fix the problem. A permanently attached flash hider or muzzle brake is itself a listed feature on the rifle side, so removing the threads while leaving the device on may not save the classification.1Washington State Legislature. Washington Code 9.41.010 – Definitions
Penalties
Violating the assault weapon ban is a gross misdemeanor.3Washington State Legislature. RCW 9.41.390 – Assault Weapons Manufacturing, Importing, Distributing, Selling Prohibited Under Washington’s sentencing framework, a gross misdemeanor carries up to 364 days in county jail and a fine of up to $5,000.5Washington State Legislature. Washington Code 9A.20.021 – Maximum Sentences for Crimes Committed July 1, 1984, and After Other firearms offenses under RCW 9.41.190, covering machine guns, short-barreled rifles, and undetectable firearms, carry different and more severe penalties, so the exact classification of your firearm matters.
Suppressors and Other Muzzle Devices
Threaded barrels exist largely to accept muzzle devices, so the legality of those devices matters. Washington permits civilian ownership and use of suppressors, provided they are legally registered under federal law.6Washington State Legislature. Washington Code 9.41.250 – Dangerous Weapons Penalty Suppressors have been legal for hunting in Washington since 2011.
Acquiring a suppressor still requires compliance with the National Firearms Act. That means submitting ATF Form 4 and passing a background check through the National Instant Criminal Background Check System.7Bureau of Alcohol, Tobacco, Firearms and Explosives. 27 CFR Part 479 – Machine Guns, Destructive Devices, and Certain Other Firearms As of January 1, 2026, the federal transfer tax for suppressors dropped from $200 to $0. The $200 tax remains only for machine guns and destructive devices.8Office of the Law Revision Counsel. 26 USC 5811 – Transfer Tax You still complete the full application and background check.
Flash hiders, muzzle brakes, and compensators aren’t independently banned in Washington. You can own them and attach them to firearms without additional registration. Just remember that a flash suppressor or muzzle brake attached to a semi-automatic center-fire rifle with a detachable magazine is itself a listed feature on the assault weapon list, exactly like a threaded barrel.1Washington State Legislature. Washington Code 9.41.010 – Definitions
Traveling Through Other States
If you drive out of Washington with a firearm that has a threaded barrel, federal law provides limited protection when passing through states with stricter rules. The Firearm Owners Protection Act lets you transport a firearm through any state so long as the firearm is legal where you start and where you’re going, the gun is unloaded, and neither the firearm nor ammunition is readily accessible from the passenger compartment. In vehicles without a separate trunk, the firearm has to be in a locked container other than the glove compartment or center console.9Office of the Law Revision Counsel. 18 USC 926A – Interstate Transportation of Firearms This covers pass-through travel. Overnight stops or extended stays in a state that bans your firearm’s configuration probably fall outside the safe-passage protection.