quote:

Overall length is measured between the extreme ends of the gun, along a centerline which passes through the middle of the barrel. For rifles fitted with folding or telescoping stocks (such as U.S. Carbine M1A1), US Federal guidelines state that measurement is made with the stock unfolded as intended for use as a rifle; exception is made for rifles with easily detachable shoulder stocks, which shall be measured with shoulder stock detached

quote:

Firearm. (a) A shotgun having a barrel or barrels of less than 18 inches in length; (b) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length; (c) a rifle having a barrel or barrels of less than 16 inches in length; (d) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length; (e) any other weapon, as defined in this subpart; (f) a machine gun; (g) a muffler or a silencer for any firearm whether or not such firearm is included within this definition; and (h) a destructive device. The term shall not include an antique firearm or any device (other than a machine gun or destructive device) which, although designed as a weapon, the Director finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector's item and is not likely to be used as a weapon. For purposes of this definition, the length of the barrel having an integral chamber(s) on a shotgun or rifle shall be determined by measuring the distance between the muzzle and the face of the bolt, breech, or breech block when closed and when the shotgun or rifle is cocked. The overall length of a weapon made from a shotgun or rifle is the distance between the extreme ends of the weapon measured along a line parallel to the center line of the bore.(emphasis added- GeorgeS).