Which firearm accessory may be possessed by a citizen with a proper license?

The possession of a trigger crank is permissible for a citizen with a proper firearm license in Massachusetts. A trigger crank allows for rapid-fire shooting by mechanically modifying how a shooter interacts with the firearm’s trigger. As a firearm accessory, it does not alter the classification of the firearm itself or make it operate as an automatic weapon.

In contrast, other accessories like silencers are heavily regulated and typically require a separate federal license under the National Firearms Act when they are legally permitted. Laser sights are often legal to possess, but they can sometimes have restrictions based on the local laws governing firearms. A grenade launcher, on the other hand, is classified as a destructive device under federal law, making it illegal for civilian possession without special licensing.

Thus, possessing a trigger crank, given the right licensing, is in line with the legal framework and regulations governing civilian firearms in Massachusetts, making it the correct choice.