I bought an old hammergun & cut the barrels to 18 1/2” with chop saw. Add swivels & I had a “lupara”, or Sicilian sawed off. Perfectly legal.
I had a Rossi coachgun. I can’t remember the barrel length but it might have been 20 inches or maybe 18.
I liked it but those Luparas carried by the bodyguards looked like expensive shotguns.