I am also not a legal expert, but I did some research and I believe the law that you are referring to is this one.
37-522. Shotgun on highway; restrictions; violation; penalty.
It shall be unlawful to have or carry, except as permitted by law, any shotgun having shells in either the chamber, receiver, or magazine in or on any vehicle on any highway. Any person violating this section shall be guilty of a Class III misdemeanor and shall be fined at least fifty dollars
Section 37 deals with Game and Parks (i.e. Hunting) and dose not define what a shotgun is.
I was not able to find a legal definition of a shotgun anywhere in the Nebraska statues, so I went looking into Federal Statues and the definitions used in US Code 26 and information regarding pistol grip firearms issued to FFL's by the ATF in Nov 2009 (included below).
Based on US Code 26 it would seem that the current legality of firearms with barrels less then 18" firing shotgun ammo is based on a ATF interpretation of the current law. The reason they are not classified as a short barreled shotgun is that they were manufactured with a pistol grip and have never had a stock attached, they have a overall length of at least 26" and are not capable of being concealed on a person change any of these conditions and they are considered a short barreled shotgun and subject to the NFA.
Handguns with rifled barrels firing shot cartridges do not fit the definition of a shotgun due to not having a smooth bore.
However, under Nebraska law (28-1201, (1) and (2)) they fit the definition of a handgun (included below).
Based on this, it would appear it would be considered a handgun by Nebraska however if it was concealed then it would be considered a short barreled shotgun by Federal Law. Please keep in mind this is not a legal opinion just the results of what I found when I researched the topic.
Personally I would not want to be the individual that gets to put this to the test.
John K
Section 28 which deals with Crime and Punishment has the following information.
28-1201. Terms, defined.
For purposes of sections 28-1201 to 28-1212.04, unless the context otherwise requires:
(1) Firearm means any weapon which is designed to or may readily be converted to expel any projectile by the action of an explosive or frame or receiver of any such weapon;
(3) Handgun means any firearm with a barrel less than sixteen inches in length or any firearm designed to be held and fired by the use of a single hand;
(7) Machine gun means any firearm, whatever its size and usual designation, that shoots automatically more than one shot, without manual reloading, by a single function of the trigger;
(9) Short rifle means a rifle having a barrel less than sixteen inches long or an overall length of less than twenty-six inches; and
(10) Short shotgun means a shotgun having a barrel or barrels less than eighteen inches long or an overall length of less than twenty-six inches.
U.S. Code 26, Chapter 53 Machineguns, Section 5845 Definitions states the following,
(a)Firearm - The term “firearm” means (1) a shotgun having a barrel or barrels of less than 18 inches in length; (2) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length; (3) a rifle having a barrel or barrels of less than 16 inches in length; (4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length; (5) any other weapon, as defined in subsection (e); (6) a machinegun; (7) any silencer (as defined in section 921 of title 18, United States Code); and (
a destructive device. The term “firearm” shall not include an antique firearm or any device (other than a machinegun or destructive device) which, although designed as a weapon, the Secretary finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector’s item and is not likely to be used as a weapon.
(d)Shotgun - The term “shotgun” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed shotgun shell to fire through a smooth bore either a number of projectiles (ball shot) or a single projectile for each pull of the trigger, and shall include any such weapon which may be readily restored to fire a fixed shotgun shell.
(e)Any other weapon - The term “any other weapon” means any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive, a pistol or revolver having a barrel with a smooth bore designed or redesigned to fire a fixed shotgun shell, weapons with combination shotgun and rifle barrels 12 inches or more, less than 18 inches in length, from which only a single discharge can be made from either barrel without manual reloading, and shall include any such weapon which may be readily restored to fire. Such term shall not include a pistol or a revolver having a rifled bore, or rifled bores, or weapons designed, made, or intended to be fired from the shoulder and not capable of firing fixed ammunition.
I was also able to find the following discussion in the Nov 2009 FFL Newsletter published by the ATF
Pistol Grips and Shotguns
Firearms with pistol grips attached: The definition of a shotgun under the GCA, 18 U.S.C. § 921(a)(5), is “a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of an explosives to fire through a smooth bore either a number of ball shot or single projectile for each single pull of the trigger. Under the GCA, 18 U.S.C. § 921(a)(29)(A), handgun means “a firearm which has a short stock and is designed to be held and fired by the use of a single hand.” Federal law provides under 18 U.S.C. 922(b)(1), that if the firearm to be transferred is “other than a rifle or shotgun,” the purchaser must be 21 years of age or older.
Certain commercially produced firearms do not fall within the definition of shotgun under the GCA even though they utilize a shotgun shell for ammunition. For example, firearms that come equipped with a pistol grip in place of the buttstock are not shotguns as defined by the GCA.
A firearm with a pistol grip in lieu of the shoulder stock is not designed to be fired from the shoulder and, therefore, is not a shotgun. Since it is a firearm “other than a rifle or shotgun,” the purchaser must be 21 years of age or older. Additionally, interstate controls apply. The licensee and transferee must be residents of the same State.
Other questions raised pertain to entries made in the licensee’s required records with respect to firearm “type.” These entries should indicate the firearm type as “pistol grip firearm.”
Age Restriction & Interstate Transfer Requirements
Licensees are reminded that firearm frames, receivers, and other firearms that are neither handguns nor long guns (rifles or shotguns) are considered “Other Firearms.” They cannot be sold or delivered by a licensee to any person under 21 years of age. Additionally, 18 U.S.C. 922(b)(3) states that a licensee shall not sell or deliver any firearm other than a shotgun or rifle to any person who does not reside in the State in which the licensee’s place of business or activity is located; this restriction includes handguns, pistol grip firearms utilizing shotgun ammunition, and frames and receivers.
