Massachusetts: List of Approved Firearm Locking Devices M.G.L. c. 140, § 131K requires that any firearm or large capacity weapon sold within the Commonwealth must be sold with a safety device designed to prevent the discharge of such weapon by unauthorized users. The following locking devices have been approved by the Colonel of the Department of State Police as complying with the provisions of M.G.L. c. 140, § 131K.