This is for the benefit of the Forum members that missed the link I providex on Page 3 to the article on the current issue of the American Rifleman:
"First, a little legal background. The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), defines a shotgun as "a weapon ... intended to be fired from the shoulder." To retain the federal classification of "shotgun," such firearms must have a barrel at least 18" in length. At that point, the stock can be replaced with a pistol grip to help shave things down, provided the overall length is not less than 26". The result is still quite sizeable, making it tough to wield in confined spaces. If you want a shorter barrel while still having a shoulder stock, then there is the ATF-regulated "short-barreled shotgun" defined by the National Firearms Act of 1934 (NFA), which is all shotguns having a shoulder stock and a barrel length shorter than 18". What if there is no shoulder stock? Well, the NFA has a category called Any Other Weapon (AOW), defined as "any weapon or device capable of being concealed on the person," excluding pistols and revolvers. The ATF further defines this as any firearm measuring less than 26" in length. So, what if you have a shotshell-firing gun that measures more than 26" long but isn't designed to be fired from the shoulder? Well, the ATF doesn't have an NFA category that captures that configuration. Hence the "non-NFA firearm." As long as the gun remains at a length greater than 26", you have one heck of an arm with which to defend confined spaces such as tents and vehicles (provided state or local laws don't state otherwise) without the associated NFA paperwork."