John, I don't think there's any way to "prove" the perceived recoil thing. Bell's work did seem to show some pressure reduction with lengthened chambers, when shooting shells longer than the chamber. But on average only a couple hundred psi, if I remember correctly. Some people do claim improved patterns from longer cones; not sure about other performance aspects. But unlike chamber lengthening, modifying cones is pretty much benign even if there isn't any real gain.