; and (B) does not include— (i) a slide that partially or completely encloses the barrel; or (ii) an extension of the stock along the bottom of the barrel which does not encircle or substantially encircle the barrel. (41) The term detachable ammunition feeding device means an ammunition feeding device that can be removed from a firearm without disassembly of the firearm action. (42) The term fixed ammunition feeding device 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. (43) 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. (44) The term forward grip means a grip located forward of the trigger that functions as a pistol grip. (45) The term grenade launcher means an attachment for use on a firearm that is designed to propel a grenade or other similar destructive device. (46) The term pistol grip means a grip, a thumbhole stock or Thordsen-type grip or 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 belt-fed semiautomatic firearm means any repeating firearm that— (A) utilizes a portion of the energy of a firing cartridge to extract the fired cartridge case and chamber the next round; (B) requires a separate pull of the trigger to fire each cartridge; and (C) has the capacity to accept a belt ammunition feeding device. . (b) Prohibitions Chapter 44 of title 18, United States Code, is amended— (1) in section 922(x)— (A) in paragraph (3)(B), by striking juvenile and inserting person who is less than 25 years of age ; (B) by redesignating paragraphs (3) through (6) as paragraphs (5) through (8), respectively