Believe it or not, but pulling a case over the expander does not lengthen the case by strecthing the brass - it can however distort and cause misalignment of the neck with the rest of the case.
Case stretching is caused by excessive headspace (of the case to the chamber) and the pressure of firing stretching the case to fit the chamber*. The 375H&H headspaces on the belt but you can use the shoulder as a defacto headspace surface (just like a rimless case).
[*In a nutshell, the firing pin pushes the whole case forward and ignites the primer/powder in the process, the gas pressure forces the case brass against the chamber but the solid case head can't be expanded to grip the chamber wall so it gets pushed back against the bolt head, stretching the brass just above the case head. End result is a lengthened case and thinning of the brass abover the case head - this will eventually lead to a head separation if the same process and conditions are repeated.]
Last edited by mauserand9mm; 01/05/14.
