Chapter 135 Definitions:

“Automatic conversion”, any modification made to a firearm, including through the use of an automatic part, that allows for the automatic discharge of more than 1 shot with 1 continuous activation of the trigger or that alters or increases the rate of fire to mimic automatic fire.

“Automatic part”, any device, part or combination of parts capable of being attached to a firearm that allows for the automatic discharge of more than 1 shot with 1 continuous activation of the trigger or that increases the rate of fire of a firearm to mimic automatic fire.

“Machine gun”, a firearm, loaded or unloaded, which may automatically discharge more than 1 shot by a continuous activation of the trigger, whether originally manufactured as such or modified by automatic conversion, including through the use of an automatic part or any firearm, loaded or unloaded, which has been modified by automatic conversion to alter or increase its rate of fire to mimic automatic fire; provided, however, that “machine gun” shall include a submachine gun.

Penalty:

Chapter 269, Section 10

...shall be punished by imprisonment in the state prison for life, or for any term of years provided that any sentence imposed under the provisions of this paragraph...

BATFE Bulletin

Fact Sheet

This is an important message from the Bureau of Alcohol, Tobacco, Firearms and Explosives. All FFLs should be aware that Machinegun Conversion Devices (MCDs) is a part, or a combination of parts, designed to modify a semi-automatic firearm so it is capable of firing automatically more than one shot by a single function of the trigger. These devices, often called switches, chips, auto sears are considered machineguns under the law. The possession, manufacture, and/or sale of machinegun conversion devices without proper licensing is a federal offense.