; or (ii) an extension of the stock along the bottom of the barrel which does not encircle or substantially encircle the barrel. (39) The term detachable magazine means an ammunition feeding device that can be removed from a firearm without disassembly of the firearm action. (40) The term fixed magazine means an ammunition feeding device that is permanently fixed to the firearm in such a manner that it cannot be removed without disassembly of the firearm. (41) The term folding, telescoping, or detachable stock means a stock that folds, telescopes, detaches or otherwise operates to reduce the length, size, or any other dimension, or otherwise enhances the concealability, of a firearm. (42) The term forward grip means a grip located forward of the trigger that functions as a pistol grip. (43) The term rocket means any simple or complex tubelike device containing combustibles that on being ignited liberate gases whose action propels the tube through the air and has a propellant charge of not more than 4 ounces. (44) The term grenade launcher or rocket launcher means an attachment for use on a firearm that is designed to propel a grenade, rocket, or other similar destructive device. (45) The term permanently inoperable means a firearm which is incapable of discharging a shot by means of an explosive and incapable of being readily restored to a firing condition. (46) The term pistol grip means a grip, a thumbhole stock, or any other characteristic that can function as a grip. (47) The term threaded barrel means a feature or characteristic that is designed in such a manner to allow for the attachment of a device such as a firearm silencer or a flash suppressor. (48) The term qualified law enforcement officer has the meaning given the term in section 926B. (49) The term grandfathered semiautomatic assault weapon means any semiautomatic assault weapon the importation, possession, sale, or transfer of which would be unlawful under section 922(v) but for the exception under paragraph (2) of such section. (50) The term