Locking mechanisms for and methods of securing firearm components in the shoulder stock or butt and/or handgrip of a collapsible firearm. In one example, the locking mechanism may include one or more locking members and a locking mechanism. In another example the locking mechanism may include a cylinder lock. The locking mechanism is configured to secure one or more firearm components in place within a storage compartment of the shoulder stock or butt and/or handgrip of the collapsible firearm, and/or to secure an endcap of the collapsible firearm to the shoulder stock or butt and/or handgrip, thereby rendering the storage compartment a locked container, with the one or more firearm components locked therein.