MGL Chapter 140, Section 121D:
3D Printer and CNC Regulations

Massachusetts General Laws Chapter 140, Section 121D^[1], created by Chapter 135 of the Acts of 2024^[2], regulates the use of 3D printers and CNC milling machines in connection with firearm manufacturing. It creates use restrictions and sale or transfer prohibitions, but it does not create a general equipment registry.

Key Prohibitions

• Use restriction: No person may use a 3D printer or CNC milling machine to manufacture or assemble any firearm without a valid License to Carry (LTC) under Section 131.
• Sale restriction: No person may sell, offer to sell, or transfer a 3D printer or CNC machine that has the "primary or intended function" of manufacturing firearms.

A machine "has the primary or intended function" of manufacturing firearms if it is "advertised, marketed or promoted to manufacture or assemble firearms, regardless of whether the printer or machine is otherwise described or classified as having other functions or as a general-purpose printer or machine."

Penalties

Imprisonment for not more than 1 year, or a fine of not more than $5,000 per firearm per violation, or both.

Exceptions

• Machines possessed by forensic laboratories
• Machines being delivered to law enforcement for destruction
• Machines possessed by common carriers during regular transport
• Machines possessed by or sold to federally licensed manufacturers
• Property of the United States government

Related Provisions

Section 121C establishes firearm serialization requirements, including for privately made firearms.^[3] Section 121B governs registration of firearms manufactured through these methods.^[4] These are firearm requirements, not registration of the printer or mill itself. Section 121D(a) itself establishes the LTC prerequisite for using the equipment to manufacture or assemble a firearm. Section 131 governs issuance and scope of the LTC.

Referendum Status

Created by Chapter 135, this section would be repealed if the November 2026 referendum succeeds.