; and (ii) any one of the features described in subsection (b); (5) the term machinegun has the meaning given such term in section 5845(b) of the Internal Revenue Code of 1986; (6) the term semiautomatic pistol means any repeating pistol that utilizes a portion of the energy of a firing cartridge to extract the fixed cartridge case and chamber the next round and requires a separate pull of the trigger to fire each cartridge; (7) the term semiautomatic rifle has the meaning given such term in section 921(a)(28) of title 18, United States Code; and (8) the term semiautomatic shotgun means any repeating shotgun that utilizes a portion of the energy of a firing cartridge to extract the fixed cartridge case and chamber the next round and requires a separate pull of a trigger to fire each cartridge. (b) Special features of a semiautomatic pistol The special features described in subsection (a)(3)(B)(ii) are— (1) an ammunition magazine that attaches to the pistol outside of the pistol grip; (2) a threaded barrel capable of accepting a barrel extender, flash suppressor, forward handgrip, or silencer; (3) a shroud that is attached to, or partially or completely encircles, the barrel and that permits the shooter to hold the firearm with the nontrigger hand without being burned; (4) a second hand grip; (5) a manufactured weight of 50 ounces or more when the pistol is unloaded