Short-barreled rifle (SBR) is a legal designation in the United States, referring to a shoulder-fired, rifled firearm, made from a rifle, with a barrel length of less than 16 in (41 cm) or overall length of less than 26 in (66 cm), or a handgun fitted with a buttstock and a barrel of less than 16 inches length. In the United States, an SBR is an item regulated by the Bureau of Alcohol, Tobacco, Firearms and Explosives (BATFE) as a Title II weapon. In the absence of local laws prohibiting ownership, American civilians may own an SBR provided it is registered with the BATFE, and a $200 tax is paid prior to taking possession of or creating the firearm.
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 performed 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 the shoulder stock detached. Some states — such as California and Michigan — measure overall length with the stock folded. Barrel length is measured from the end of the muzzle to the front of the breechface, typically by inserting a measuring rod into the barrel. Barrel length may partially comprise a permanently attached muzzle accessory (such as a recoil compensator or flash suppressor).
SBRs may be created by trimming down a larger rifle, by building a rifle with an original barrel shorter than 16 in (41 cm), or by adding a shoulder stock to a handgun which is fitted with a barrel shorter than 16 in (41 cm), thereby legally redefining it as a rifle rather than a handgun. Each of these processes must legally be accompanied by ATF registration. Certain old handguns originally available with shoulder stocks, such as original broomhandle Mausers or Lugers manufactured before 1946, more likely to be valued as curios or relics than as weapons, have been removed from federal SBR restriction but may be restricted under local gun laws. Certain "trapper model" rifles manufactured before 1934 with barrels under 16 in (41 cm) have similarly been removed from federal SBR restriction (the ATF publishes a Curios and Relics List of models and serial number ranges). While SBRs on the Curio & Relic List are not "firearms" regulated under the 1934 National Firearms Act, they are still "firearms" regulated by the Gun Control Act of 1968.
In the United States, it is a federal felony to possess an SBR unless it is registered with the ATF to the person who possesses it. Class 2 manufacturers, Class 3 dealers and government agencies will transfer these firearms tax exempt but individuals must pay a tax of $200 to manufacture or transfer an SBR. ATF notification is required when transporting an SBR across state lines; this is accomplished by filing Form 5320.20 in advance of the travel date. SBRs may not be taken into states where they are prohibited except with prior approval from the ATF.
Purchasing a short-barreled rifle is accomplished by finding the item desired, paying for it and then arranging for the transfer of the registered item. An individual will be required to file a ATF Form 4, Application for Tax Paid Transfer and Registration of a Firearm, and paying a $200 tax. A short-barreled rifle must be transferred by a Class 3 or a Class 2 SOT dealer if the transfer will be across state lines. For transfers within a state the transfer may be accomplished by the individuals involved though the $200 transfer tax is still due. For transfers between dealers or manufacturers the Form 3- application for tax exempt transfer is filled out. For transfers to or from govt agencies (police departments, et al.) a Form 5 is used for tax exempt transfer to dealers or individuals(there is no tax due on transfers to or from govt agencies). When an individual wishes to build a short-barreled rifle, he or she must beforehand submit a completed ATF Form 1, Application to Make and Register a Firearm, along with $200 for payment of the making tax.
As a result of the Supreme Court decision in United States v. Thompson/Center Arms Company, 504 U.S. 505 (1992), it is not illegal to possess a "kit" allowing a handgun to be fitted with a buttstock and with barrels both under and over the 16 inch minimum for a rifle, so long as the firearm is only assembled into legal (handgun with no buttstock, rifle with buttstock and 16 inch or longer barrel) configurations. Assembling into an NFA-regulated configuration (rifle with buttstock but barrel shorter than 16 inches) would still constitute a criminal violation of the National Firearms Act.