I have a .376/06IMP with a .460" shoulder and .470" base. Yes - you would need a new reamer - that's the name of the game with IMP chamberings.

I had not thought of nor would never think of re-chambering the Mann. as that would be foolish, however anyone wanting to make one up on a Mauser action, could easily do this.

I guess I wasn't explicit enough in my post. This was also before I remembered the larger shoulder diameter of the 9.5x57, pretty close to standard to an Ackley Chamber. This was again brought home through the diagrams & measurements.

The Ackley chamber is only .454" - same as my 9.3x62 is, a factory Mauser and at least one other 9.3x62I know of, a client's Styer rifle 9.3x62, not .451" as the cip #'s I saw, go.