You can have one custom made by a class 3 manufacturer. It has to be registered in the national firearms registry as an AOW. I am currently in the process of having a 15" 20 ga. Encore pistol barrel made to turkey hunt with. It's illegal to own a shotgun with barrel less than 18" unless you go through the correct procedures.

It takes 43 muscles to frown and 17 to smile, but only 3 for proper trigger squeeze.