Here are the wall thickness measurements out to 21"

Right bbl : 3"-.1325, 6"-.082, 9"-.0595, 12"-.042, 15"-.033, 18"-.0285, 21"-.027

Left bbl : 3"-.1205, 6"-.0735, 9"-.052, 12"-.0405, 15"-.0305, 18"-.026, 21"-.0245


I wish I were a better picture taker. Thanks for the help thus far.