I could be wrong, but I think that I remember that the shotgun has to have a barrel of at least 18" and an overall length of 31". I could be wrong, but you might want to check this out. That is why I put a pistol gripped buttstock on my 12 gauge with the 18.5" barrel.
Also for the OP from US code [FONT=verdana, arial, helvetica][SIZE=-1]Sec. 5845.[/SIZE][/FONT][FONT=verdana, arial, helvetica][SIZE=-1](5) 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 an explosive to fire through a smooth bore either a number of ball shot or a single projectile for each single pull of the trigger.[/SIZE][/FONT]
[FONT=verdana, arial, helvetica][SIZE=-1](6) The term "short-barreled shotgun" means a shotgun having one or more barrels less than eighteen inches in length and any weapon made from a shotgun (whether by alteration, modification, or otherwise) if such weapon as modified has an overall length of less than twenty-six inches.[/SIZE][/FONT]
Barrel is 18" so its open game on dual grips. Unless someone can cite law that says otherwise. But length is key, if its a 18+" barrel and 26+" overall it is legally impossible for the gun for be a SBS or AOW without a hacksaw. AOW or SBS laws only apply if you want to hack the barrel down.(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.