Daryl, 9.5x57 M-S cases from my M1910 have a shoulder diameter of 11.6 mm = .456", already more than an "Ackley Improved" shoulder, according to your numbers. In a former thread I wrote the 9.5x57 M-S already being sort of an "improved" case, compared to the other x57 Mauser numbers. You suggested then "improving" the 9.5x57 M-S aka .375 Rimless NE further. Well, you would need a special reamer and special reloading dies. You would end up with just another wildcat noone else wants and a buggered collectors piece. The gains would most likely be less than 5% in powder capacity and ballistics. IMHO this is not worth all the fuss. If I want more oomp! I'll grab my 9.3x62, 9.3x74R (not much practical gain here) or my .416 Rigby instead.