Here is an article that I wrote for Mossberg recently explaining the legal differences between “shotguns,” “any other weapons,” and “pistol-grip firearms.” In the examples in the article, they all shoot shotgun shells but they are very different under the law. Check out the full article on Mossberg.com
Most people assume that a firearm that shoots shotgun shells is a shotgun. As far as the federal law is concerned, however, this isn’t necessarily true.
There are two main categories of standard firearms: long-guns and handguns. Long-guns are firearms that are designed and intended to be fired from your shoulder and are at least 26 inches in overall length. Therefore, if the firearm has a buttstock and is long enough, it is a “long-gun.” However, if the firearm is instead designed to be fired from one hand, then it is a handgun.
There are two sub-categories of long-guns: shotguns and rifles. A shotgun is a long-gun that has a smooth barrel, and a rifle is a long-gun that has a rifled barrel. Therefore, if a firearm has a buttstock, it is over 26 inches long, and it has a smooth barrel, it is a shotgun. If any of those variables change, then the firearm is no longer considered a shotgun under federal law.
Mossberg offers two different types of firearms which are built on shotgun receivers and that fire shotgun shells that aren’t technically shotguns. These are certain models of Mossberg 500s and 590s which have pistol grips without buttstocks and an overall length under 26 inches (Any other Weapons) or over 26 inches (Pistol Grip Firearms).
“Any Other Weapons”
As you’re likely aware, there’s a whole special category of firearms sometimes called “National Firearms Act (NFA) firearms.” This category of firearms includes certain categories of highly-regulated firearms such as short-barreled shotguns (SBS) and “any other weapons” (AOW).
An SBS is a shotgun that has a barrel length less than 18 inches and/or an overall length less than 26 inches. Therefore, if it has a buttstock and a smooth barrel but either the barrel or the overall length aren’t long enough, then it is regulated as an SBS. . .