A binary trigger fires one bullet when you pull it and another when you release it.
These triggers are typically aftermarket components.
In most states, binary triggers are legal.
However, in Massachusetts, binary triggers are tantamount to machine guns.
The machine gun statute–G.L. c. 269, Sec. 10(c)–prohibits machine guns as well as “trigger modifiers.”
In October 2024, the legislature revised the statutory law, expressly defining the term “trigger modifier” as
any modification that repeatedly activates the trigger of a firearm, including, but not limited to, trigger cranks, binary triggers and hellfire triggers.
Those convicted of violating G.L. c. 269, Sec. 10(c), face a mandatory minimum sentence of 18 months in the house of corrections.