This is a dumb question and my first post but according to the batfe as long as the gun stays over 26in can't you cut down the barrel down more than 18 and still be legal?
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), without a tax-paid registration