Massachusetts HD 4420: Assault Weapons, Ghost Guns, and Storage Rules

Massachusetts HD 4420 is the original House filing that became Chapter 135 of the Acts of 2024, the state’s overhaul of its firearm laws. Filed by Representative Michael S. Day of Stoneham on June 26, 2023 as “An Act modernizing firearm laws,” it was reshaped through the legislative process and signed by Governor Healey with a general effective date of October 23, 2024. Several provisions phase in through 2026.¹ When people say “HD 4420” today, they usually mean the enacted law, not the original draft.

The law broadens what counts as an assault-style firearm, requires every firearm in the state to be serialized and registered through new electronic systems, raises the age for a license to carry to 21, adds a live-fire training requirement, and increases penalties for unsafe storage.

What Counts as an Assault-Style Firearm Now

The old “assault weapon” definition is gone. In its place is a broader “assault-style firearm” category built on a two-feature test. A semiautomatic centerfire rifle that accepts a detachable magazine qualifies if it has at least two of the following: a folding or telescoping stock, a thumbhole stock or pistol grip, a forward grip, a threaded barrel designed for a flash suppressor, or a barrel shroud designed to shield the shooter’s hand from heat.²

Similar two-feature tests apply to semiautomatic pistols and shotguns, each with its own feature list. Separately, the state maintains an “assault-style firearm roster,” and any firearm on that roster qualifies regardless of features.²

If you lawfully possessed an assault-style firearm in Massachusetts before August 1, 2024, you can keep it. But you have to register and serialize it through the new system.³

Registration and Serialization

The law creates two new statewide electronic systems: a firearms registration system under Section 121B and a serialization request system under Section 121C. Massachusetts had one year from the effective date to build each system, and firearm owners then have one year after each system launches to comply.¹

The hard deadline for serialization is October 2, 2026. That applies to any unserialized firearm or any frame or receiver that could readily be converted into one. New unserialized firearms brought into Massachusetts must be reported within seven days.

3D-printed polymer firearms carry a specific requirement. Engraving a serial number on the polymer itself is not sufficient. The law requires embedding a three-ounce stainless steel plate so that the serial number is permanently engraved on metal.

Ghost Guns

Untraceable firearms built from parts kits or 3D printing, often called ghost guns, are now directly covered. Possessing an unserialized firearm that has not been registered through the state’s system is a crime, and owners of existing ghost guns must bring them into compliance through the DCJIS electronic serialization process. The state requirement runs parallel to a 2022 federal rule and reaches further, because Massachusetts demands electronic registration with the state rather than compliance only at the point of sale.⁴

Safe Storage and Penalties

Every firearm must be stored in a locked container or fitted with a tamper-resistant mechanical lock that renders it inoperable to anyone other than the owner or an authorized user. A firearm you are actively carrying or that is under your direct control is not “stored” for purposes of the statute.⁵

Penalties scale with the type of firearm and whether a minor could reach it:

Standard firearm: $1,000 to $7,500 fine, up to 1.5 years imprisonment, or both.
Large capacity or semiautomatic weapon: $2,000 to $15,000 fine, 1.5 to 12 years imprisonment, or both.
Any firearm accessible to a minor under 18 who does not hold a valid firearm identification card: $2,500 to $15,000 fine, 1.5 to 12 years imprisonment, or both.
Large capacity weapon accessible to a minor: $10,000 to $20,000 fine, 4 to 15 years imprisonment, or both.

A safe storage violation also counts as evidence of reckless conduct in any criminal or civil case where a minor gains access to the firearm and someone is injured or killed.⁵

Age and Licensing

The minimum age for a license to carry is now 21. A firearm identification card, which allows possession of non-large-capacity rifles and shotguns, is available at age 15 with the written permission of a parent or guardian. A 14-year-old may apply, but the card is not issued until they turn 15.²

Because semiautomatic rifles and shotguns now require a license to carry rather than a firearm identification card, people under 21 cannot purchase or possess them. Adults aged 18 to 20 can still own non-semiautomatic firearms with a firearm identification card. People under 18 can use firearms under the direct supervision of a licensed adult for hunting, instruction, recreation, and shooting sports.

Training Requirements

Certified instructors must now teach a curriculum covering safe use, handling and storage, childproofing, laws on possession and transportation, use of force, injury and suicide prevention, disengagement tactics, and live firearms training.²

The live-fire component is the significant change. Prior law permitted classroom-only courses. The live-fire requirement must take effect by April 2026. Anyone who already held a firearm identification card or license to carry as of August 1, 2024 is exempt from the live-fire requirement, including at renewal.⁶

Firearms dealers have their own mandate. An online dealer training program developed by the Executive Office of Public Safety and Security must be completed before a licensing authority will process a dealer application.²

Court Challenges

The law is in effect and being litigated. Challenges lean on the U.S. Supreme Court’s 2022 decision in New York State Rifle & Pistol Association v. Bruen, which requires firearm regulations to fit within the American historical tradition of firearm regulation.

In Marquis v. Commonwealth of Massachusetts, the plaintiff argued that the state’s concealed carry permit system operates as a “may issue” regime because the state police colonel retains discretion. In March 2025, the Massachusetts Supreme Judicial Court ruled that the permitting law survives Bruen, finding that requiring “credible, individualized evidence that the person in question would pose a danger if armed” is consistent with the historical tradition. The case is being appealed to the U.S. Supreme Court, with attorneys general from more than 25 states filing a brief supporting the challenger. How far Bruen reaches into state licensing, registration, and training requirements is still being tested.

Travel Into and Out of Massachusetts

Federal law protects people who transport a firearm between two states where they can lawfully possess it. The firearm must be unloaded, and neither the firearm nor the ammunition may be readily accessible from the passenger compartment. In a vehicle without a separate trunk, both must be in a locked container that is not the glove compartment or center console.⁷

This matters because a firearm that is legal in New Hampshire or Vermont may violate Massachusetts law if it is unregistered or unserialized. Federal safe-passage protection covers travelers passing through. It does not cover someone who stops in the state for an extended stay or who is not traveling between two places where possession is lawful.

Compliance Timeline

The general effective date was October 23, 2024. Several provisions run on their own clocks:¹

Electronic registration system: state build target of roughly October 2025, then one year for owners to register once the system is publicly available.
Serialization system: same one-year build window, with a hard compliance deadline of October 2, 2026 for all unserialized firearms.
Live-fire training: must be in effect by April 2026.⁶
Dealer training for licensing authorities: takes effect 18 months after the effective date, roughly April 2026.²

The compliance clocks for registration and serialization start only when each system goes live. The Executive Office of Public Safety and Security and the DCJIS are the agencies building and operating them, and their launch announcements are the dates to watch.

1
Mass.gov. An Act Modernizing Firearms Laws – Effective Dates
2
General Court of Massachusetts. Acts of 2024, Chapter 135
3
Mass.gov. Massachusetts General Laws Chapter 140 Section 131M
4
Bureau of Alcohol, Tobacco, Firearms and Explosives. Definition of Frame or Receiver and Identification of Firearms
5
General Court of Massachusetts. Massachusetts General Laws Chapter 140 Section 131L
6
Mass.gov. Section 152 Live Firearms Report
7
Office of the Law Revision Counsel. 18 U.S. Code 926A – Interstate Transportation of Firearms