Massachusetts firearm law uses specific statutory definitions that may be different from ordinary firearm terminology or federal definitions.
Before applying a Massachusetts firearm law, first determine how Massachusetts defines the firearm, component, feeding device, or activity involved.
Massachusetts Gun Law Definitions
Most of the definitions used throughout Massachusetts firearm law are contained in M.G.L. c. 140, §121.
These definitions can determine what license is required, whether an item must be registered or serialized, whether a firearm is considered large-capacity or assault-style, and whether a statutory exception applies.
Find a Definition
Enter a word such as firearm, receiver, magazine, semiautomatic, antique, large capacity, or serial number.
Firearm Definitions
Firearm
Core Definition M.G.L. c. 140 §121Massachusetts defines "firearm" broadly to include a stun gun, pistol, revolver, rifle, shotgun, sawed-off shotgun, large-capacity firearm, assault-style firearm, and machine gun, whether loaded or unloaded, that is designed to or may readily be converted to expel a shot or bullet.
The definition also includes the frame, receiver, or unfinished frame or receiver of such a firearm.
Antique firearms and permanently inoperable firearms are excluded from this definition when they satisfy the applicable statutory requirements.
Rifle
A firearm having a rifled bore with a barrel length of 16 inches or greater and capable of discharging a shot or bullet for each pull of the trigger.
Shotgun
A firearm having a smooth bore with a barrel length of 18 inches or greater, an overall length of 26 inches or greater, and capable of discharging a shot or bullet for each pull of the trigger.
Sawed-Off Shotgun
A firearm made from a shotgun that, after alteration or modification, has one or more barrels shorter than 18 inches or an overall length shorter than 26 inches.
Machine Gun
Massachusetts generally defines a machine gun as a firearm that can automatically discharge more than one shot through continuous activation of the trigger.
The definition also includes certain firearms modified through automatic conversion or modified to alter or increase their rate of fire to mimic automatic fire.
Antique Firearm
The Massachusetts antique-firearm definition generally includes qualifying firearms or replicas manufactured in or before 1899, subject to the ammunition requirements contained in §121.
It can also include certain muzzleloading rifles, shotguns, and pistols designed for black powder or black-powder substitutes that cannot use fixed ammunition.
Frames, Receivers & Components
Frame
Massachusetts generally defines a frame as the part of a pistol or revolver that provides the housing or structure for the component designed to hold back the hammer, striker, bolt, or similar primary energized component before the firing sequence begins.
Receiver
Massachusetts generally defines a receiver as the part of a rifle or shotgun providing the housing or structure for the primary component designed to block or seal the breech before the firing sequence begins.
Unfinished Frame or Receiver
A forging, casting, printing, extrusion, machined body, or similar item that has reached a stage where it may readily be completed or assembled to function as a frame or receiver.
The definition can also include an item marketed or sold to become or be used as the frame or receiver of a functional firearm once completed or assembled.
A component designed and intended for use in an antique firearm is excluded.
Privately Made Firearm
A firearm manufactured or assembled by an individual who is not a licensed manufacturer.
The definition excludes firearms manufactured or assembled by persons licensed under M.G.L. c. 140, §122 in the course of their licensed business activities.
Feeding Devices & Capacity
Feeding Device
Any magazine, belt, strip, drum, or similar device that holds ammunition for a firearm, whether fixed or detachable.
Large-Capacity Feeding Device
Massachusetts generally defines a large-capacity feeding device as a fixed or detachable magazine, belt, drum, feed strip, or similar device capable of accepting:
- more than 10 rounds of ammunition; or
- more than 5 shotgun shells.
The definition can also include combinations of parts from which such a device can be assembled when those parts are under the possession or control of the same person.
The statute contains exclusions for certain permanently modified devices, qualifying .22 caliber tubular devices, and certain tubular magazines in lever-action firearms or pump shotguns.
Large-Capacity Firearm
Secondary DesignationMassachusetts generally defines a firearm as large-capacity when it meets one of several statutory tests, including certain semiautomatic firearms with fixed or detachable large-capacity feeding devices, certain firearms employing high-capacity rotating cylinders, and assault-style firearms.
The definition contains exclusions for certain manual-action firearms, single-shot firearms, permanently inoperable firearms, and qualifying antiques, relics, props, and similar items.
Assault-Style Firearms
Assault-Style Firearm
Massachusetts uses several different statutory tests to determine whether a firearm is an assault-style firearm.
These include feature-based tests for certain:
- semiautomatic centerfire rifles;
- semiautomatic pistols; and
- semiautomatic shotguns.
The definition also addresses specifically enumerated firearm families, copies and duplicates, and other statutory categories.
For the complete analysis, use GOAL's separate Massachusetts Assault-Style Firearm Guide.
Serialization Definitions
Untraceable Firearm
A firearm that has not been serialized, or a firearm whose serial or other identification number has been removed, defaced, altered, obliterated, or mutilated.
Valid Serial Number
An identifying number placed on a firearm by an authorized federal licensee, under applicable state law, under federal NFA requirements, or a serial number issued by ATF or the Massachusetts Department of Criminal Justice Information Services.
Permanently Embedded
Applied in a manner that cannot be easily or readily removed without destroying the part to which it is applied.
Important Action Definitions
Manufacture
To fabricate, make, form, produce, or construct a firearm by manual labor or machinery.
The statutory definition excludes firearm reassembly, firearm repair, and the making or fitting of special barrels, stocks, or trigger mechanisms to firearms.
Purchase / Sale
For purposes of §121, purchase and sale include an exchange.
The terms purchaser, sell, and purchase are interpreted accordingly.
Gunsmith
A person engaged in the business of repairing, altering, cleaning, polishing, engraving, blueing, or performing mechanical operations on firearms.
Other Important Definitions
Ammunition
Massachusetts defines ammunition to include cartridges, cartridge cases, primers, bullets, and propellant powder designed for use in firearms, rifles, or shotguns.
The statutory definition also includes tear gas cartridges.
Nonresident
A person temporarily in Massachusetts who legally resides in another state or territory of the United States.
Secured in a Locked Container
Massachusetts defines this as secured in a container capable of being unlocked only by a key, combination, or similar means.
The definition expressly includes certain circumstances involving:
- a locked trunk in an unoccupied motor vehicle that is not accessible from the passenger compartment;
- a locked console;
- a locked glovebox; and
- certain locked-access areas used by common carriers.
Automatic Conversion
A modification to a firearm, including through use of an automatic part, that allows automatic discharge of more than one shot with one continuous activation of the trigger or alters or increases the firearm's rate of fire to mimic automatic fire.
Automatic Part
A device, part, or combination of parts capable of being attached to a firearm that allows automatic discharge of more than one shot with one continuous activation of the trigger or increases the rate of fire to mimic automatic fire.
Rapid-Fire Trigger Activator
A device, part, or combination of parts designed to substantially increase the rate of fire of a semiautomatic firearm above its standard rate of fire.
The statute contains specific exclusions involving trigger-pull weight adjustments and magazine springs.
Trigger Modifier
Massachusetts defines a trigger modifier as a modification that repeatedly activates the trigger of a firearm.
The statutory definition specifically references devices including trigger cranks, binary triggers, and hellfire triggers.
Covert Firearm
Generally, a firearm placed in a camouflaging firearm container or certain firearms constructed in a shape that does not resemble or is not immediately recognizable as a firearm.
The statute provides examples and should be reviewed directly before determining whether a particular device falls within this definition.
Undetectable Firearm
Massachusetts defines certain firearms or major firearm components as undetectable based on their ability to avoid detection or accurate imaging by specified security-detection technology.
Imitation Firearm
A firearm designed, manufactured, or altered so that it is incapable of discharging a shot or bullet.
Curio or Relic Firearms
Firearms of special interest to collectors because they possess qualities not ordinarily associated with firearms intended for sporting, offensive, or defensive use.
Why Definitions Matter
Whether an item is a firearm, semiautomatic firearm, large-capacity firearm, rifle, or shotgun can affect the license required to possess it.
Frames, receivers, unfinished frames, and unfinished receivers can fall within Massachusetts' firearm definition.
The definitions of firearm, privately made firearm, unfinished frame or receiver, untraceable firearm, and valid serial number are critical.
Definitions involving large-capacity firearms, feeding devices, and locked containers can change how an item must be transported.
A firearm that is lawful to possess may still be restricted for hunting based on firearm type and hunting regulations.
Feature tests, operating systems, receivers, and copies or duplicates require separate analysis.
GOAL Guidance
Chapter 135 substantially changed Massachusetts firearm terminology. Because these definitions are used throughout the Commonwealth's firearm laws, GOAL recommends identifying the statutory classification of a firearm or component before applying licensing, possession, registration, serialization, transportation, transfer, or hunting requirements.
When GOAL's interpretation differs from an interpretation advanced by the Commonwealth, GOAL will identify that material as GOAL analysis rather than statutory language.
Primary Sources
- M.G.L. c. 140, §121 — primary Massachusetts firearm definitions.
- Chapter 135 of the Acts of 2024 — legislation establishing many of the current definitions.
- GOAL — Massachusetts Gun Law Definitions
- GOAL — Chapter 135 Resource Center
This page provides plain-language summaries for educational purposes. For the controlling legal language, review the current Massachusetts statute.
Definitions should also be read together with the particular law in which they are being applied.