It's a 12 ga that has been cut down to the 20 inch vent rib, because there isn't a vent rib post again until the 17 inch mark. They look goofy as heck cut down to 18 inches and missing one inch of vent rib... Ask me how I know.
Ah ha. Okay; I'll bite. How do you know? (Any pics of Bubba'd barrel?)