I'd get in touch with Briley-if they installed the chokes, the serial number of your "Kraut-Kannon" would be in file. A variation in Wall Thickness, worn reamers, hones, could be an out-of-round barrel where threaded for the tubes, also tubes.

If previous owner used this with steel shot loads, or shot slugs, all sorta factors. Of course, you are in Colorado- might just have been one of the "Little Deutchendorff Kid's- aka- John Denver-" personal shotguns, hence the "Rocky Mountain High"..

"The field is the touchstone of the man"..