Threaded barrels are legal in Massachusetts on their own, but state law treats a threaded barrel as a restricted feature. On a semi-automatic rifle or pistol that accepts a detachable magazine, pairing a threaded barrel with even one other listed feature turns the firearm into a prohibited “assault-style firearm.” Whether your setup is legal depends on the rest of the gun, when you acquired it, and whether you have met the registration rules.
When a Threaded Barrel Crosses the Line
Massachusetts rewrote its firearm rules in 2024 under Chapter 135, replacing the older “assault weapon” term with “assault-style firearm” and updating General Laws Chapter 140, Section 121. A semi-automatic firearm that accepts a detachable magazine becomes an assault-style firearm when it has two or more features from a prohibited list. A threaded barrel is on that list for both rifles and pistols.
For a semi-automatic centerfire rifle with a detachable magazine, the restricted features are a folding or telescoping stock, a thumbhole stock or pistol grip, a forward grip or second handgrip, a threaded barrel designed to accept a flash suppressor or muzzle brake or similar device, and a barrel shroud that shields the shooter’s hand from heat (a slide enclosing the barrel does not count).1General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 121
For a semi-automatic pistol with a detachable magazine, the restricted features are a magazine attachment outside the pistol grip, a second handgrip or protruding grip for the non-trigger hand, a threaded barrel capable of accepting a flash suppressor or forward handgrip or silencer, and a barrel shroud that shields the shooter’s hand from heat.1General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 121
In both cases, the two-feature test is what matters. A semi-automatic pistol with a threaded barrel and no other listed feature is not an assault-style firearm. A bolt-action or lever-action rifle with a threaded barrel is not either, because the feature test only reaches semi-automatics that accept a detachable magazine.
Shotguns With Threaded Barrels
Semi-automatic shotguns have their own, shorter feature list: a folding or telescoping stock, a thumbhole stock or pistol grip, a protruding grip for the non-trigger hand, and the capacity to accept a detachable magazine. A threaded barrel is not on the shotgun list.1General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 121 A threaded muzzle on a semi-automatic shotgun does not, on its own, trigger the assault-style classification.
The Fixed-Magazine Configuration
The feature test only applies to firearms with “the capacity to accept a detachable feeding device.” A rifle or pistol built around a fixed magazine that cannot be removed without disassembling the action does not clear that threshold, no matter how many listed features it carries.1General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 121 Some Massachusetts owners use this configuration to keep an otherwise noncompliant rifle legal.
The fixed-magazine route does not rescue a firearm that is banned by name or as a copy. Massachusetts separately bans specific models, including AK variants, the Colt AR-15, the Beretta AR70, the UZI and Galil, the FN/FAL and FNC, several SWD models, the Steyr AUG, the INTRATEC TEC-9 family, and revolving-cylinder shotguns like the Street Sweeper. Any firearm that qualifies as a “copy or duplicate” of a listed or rostered model is also banned, based on internal components and receiver interchangeability rather than cosmetic features.1General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 121
Suppressors Are Illegal Regardless
The most common reason to want a threaded barrel is to attach a suppressor. Civilian possession of suppressors is prohibited under Massachusetts law. Federal regulation of suppressors as National Firearms Act items, including the drop of the federal tax stamp to $0 in 2026, does not change the state prohibition. Possessing a suppressor in Massachusetts is a state crime regardless of federal paperwork. That leaves the practical use of a threaded barrel here limited to compensators, muzzle brakes, and similar devices that are not classified as silencers or flash suppressors.
Grandfathering and Registration
If you lawfully possessed an assault-style firearm in Massachusetts on or before August 1, 2024, and you held a valid license to carry under Section 131, you can keep it. You have to register it under Section 121B and have it serialized under Section 121C.2General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 131M
The 2024 law reset the grandfathering date. Previously the key date was September 13, 1994, when the federal ban took effect, and pre-1994 firearms were broadly grandfathered. Under the current statute, anything acquired after August 1, 2024 gets no grandfathering, and even grandfathered firearms face transfer restrictions. Large-capacity feeding devices lawfully possessed before September 13, 1994 keep their own separate grandfathering, with limits on where they can be possessed and who they can be transferred to.2General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 131M
Penalties for an Illegal Configuration
Possessing, selling, transferring, or importing an assault-style firearm in violation of the statute is punishable on a first offense by a fine of $1,000 to $10,000, imprisonment of one to ten years, or both. A second offense carries a minimum $5,000 fine and a minimum five years of imprisonment, with maximums of $15,000 and fifteen years.2General Court of Massachusetts. General Law – Part I, Title XX, Chapter 140, Section 131M The second-offense minimum is mandatory prison time.
Driving Through Massachusetts
If your firearm would be an illegal assault-style configuration under Massachusetts law but is legal at both ends of your trip, the federal Firearm Owners’ Protection Act allows you to transport it through the state. The firearm has to be unloaded and stored where it is not readily accessible from the passenger compartment. In a vehicle without a trunk, it must be in a locked container other than the glove compartment or console.3Office of the Law Revision Counsel. 18 U.S. Code 926A – Interstate Transportation of Firearms
The protection covers passing through, not stopping. An overnight at a hotel, a visit with friends, or errands can end the federal shield and put you under state law. Plan routes accordingly, and keep documentation of your origin and destination.