431 Definitions 431.1 Firearm The following definitions apply: a. Firearm means any device, including a starter gun, which will, or is designed to, or may readily be converted to, expel a projectile by the action of an explosive; the frame or receiver of any such weapon; any firearm muffler or firearm silencer; or any destructive device; but the term shall not include antique firearms (except antique firearms meeting the description of a handgun or of a firearm capable of being concealed on a person). b. Firearm frame or receiver is the part of a firearm which provides housing for the hammer, bolt or breechblock, and firing mechanism, and which is usually threaded at its forward portion to receive the barrel. Frames and receivers usually (but not always) include the firearm serial number and are usually considered to be the regulated component of a firearm.
431.2 Handguns Pistols, revolvers, and other firearms capable of being concealed on the person (for example, short-barreled shotguns and short-barreled rifles) are defined as handguns. The following definitions apply: a. Handgun (including pistols and revolvers) means any firearm which has a short stock, and is designed to be held and fired by the use of a single hand and subject to 431.1, or a combination of parts from which a handgun can be assembled. b. Other firearms capable of being concealed on the person include, but are not limited to, short-barreled shotguns and short-barreled rifles. c. Short-barreled shotgun means a shotgun that has one or more barrels less than 18 inches long. The term short-barreled rifle means a rifle that has one or more barrels that are less than 16 inches long. These definitions include any weapon made from a shotgun or rifle, whether by alteration, modification, or otherwise, if such a weapon as modified has an overall length of less than 26 inches. A short-barreled shotgun or rifle of greater dimension may be regarded as nonmailable when it has characteristics to allow concealment on the person.
431.3 Antique Firearm Antique firearm means any muzzle loading rifle/shotgun/pistol, which is designed to use black powder or a black powder substitute, and which cannot use fixed ammunition (except those that incorporate a firearm frame or receiver, any firearm which is converted into a muzzle loading weapon, or any muzzle loading weapon which can be readily converted to fire fixed ammunition by replacing the barrel, bolt, breechblock, or any combination 431.4 Hazardous, Restricted, and Perishable Mail 98 Publication 52 thereof); or any firearm (including those with a matchlock, flintlock, percussion cap, or similar type of ignition system) manufactured on or before 1898, or any replica thereof, if such replica: a. Is not designed or redesigned for using rimfire or conventional centerfire fixed ammunition. b. Uses rimfire or conventional centerfire fixed ammunition that is no longer manufactured in the United States and is not readily available in the ordinary channels of commercial trade.