Picked up an older Mossberg 500 ATP at a gunshow Saturday. Came with 2 barrels, both 18.5". One had been cut down from a 28" modified cylinder barrel and had been rifled, apparently by bubba as it was crudely done and wavy for the first couple of inches past the chamber. The other didn't have a length stamped on it, but it had a variable choke silver soldered on the muzzle end.
I have no idea how, or by whom that one barrel was rifled.