<P> Semi-automatic and pump action shotguns, regardless of whether they are held on shotgun or firearms certificates are always required to comply with the specification of 24" minimum barrel length, 40" minimum overall length . </P> <P> Muzzleloading firearms held on firearms certificates are exempt from any restrictions on barrel and overall length . A smoothbore muzzleloader held on a shotgun certificate would be subject to the standard 24" minimum barrel length specification . </P> <P> Under the National Firearms Act (NFA), it is illegal for a private citizen to possess a sawed - off modern smokeless powder shotgun (a shotgun with a barrel length shorter than 18 inches (46 cm) or an overall length shorter than 26 inches (66 cm)) (under U.S.C. Title II), without a tax - paid registration from the Bureau of Alcohol, Tobacco, Firearms and Explosives, requiring a background check and either a $200 or $5 tax for every transfer, depending upon the specific manufacturing circumstances of the particular sawed - off modern shotgun being transferred . Gun trusts have become an increasingly popular means of registering SBS' with the BATFE . Short - barreled muzzleloading blackpowder shotguns, in contrast, are not illegal by federal law and require no tax - stamped permit, although they may be illegal under state law . As with all NFA regulated firearms, a new tax stamp must be purchased before every transfer . Inter-state transfers must be facilitated through a Federal Firearms Licensee (FFL) while intrastate transfers may be between two persons . </P> <P> In the US, shotguns originally manufactured without shoulder stocks (and thus not legally shotguns), with a total length under 26 inches, are classified as an "Any Other Weapon" by the BATFE and have a $5 transfer tax, if they are manufactured by a maker possessing the appropriate Class 2 Special Occupational Taxpayer Federal Firearms License . In order to convert an existing shoulder - stocked shotgun to a short - barreled shotgun or an existing pistol - grip - only shotgun to an "Any Other Weapon", a private citizen must pay the standard $200 NFA tax . </P>

What is the shortest legal length of a shotgun barrel