sentences:  Barrel length may partially comprise a permanently attached muzzle accessory (such as a recoil compensator or flash suppressor).Short barreled rifles may be created by trimming down a larger rifle, by building a rifle with an original barrel shorter than , or by adding a shoulder stock to a handgun which is fitted with a barrel shorter than , thereby legally redefining it as a rifle rather than a handgun.Each of these processes must legally be accompanied by ATF registration.