Found in Doug's papers - This is a print of a Ordnance Department B&W photo (Negative #A-692) showing a M1921 barrel with small compensator and corresponding small diameter of barrel where the comp screws on. This is barrel "A" in the photo and is labelled a "standard" barrel. Barrel "B" is what we now know as a M1928 barrel and comp with the larger diameter and longer comp and the large diameter of the barrel where the comp screws on. This is the "proposed" barrel. It's too bad there is no date on this, but it is (I think) interesting.
Bob