The Smokeless powder era certainly pre-dated the Flues model. I have not owned a lot of them but as I recall all that I did own had the bbls marked "Smokeless Powder Steel". It was not smokeless powder or for that matter even chamber pressure which did in the Flues design. It was rather the introduction of newer slower burning "Progressive" smokeless powders in the 1920's which allowed heavier shot charges to be fired at full (or even higher) velocities, previously only obtainable with lighter shot loads. The design of the Flues frame was borderline for this increased thrust & some began to fail, bringing on the re-design to the NID.
