Nosler's book listed 7x57 as having a 1.728" base to shoulder measurement, ie: body length.
If the drawing of the 9.5mm Man.is correct, it is .097" longer making headspace OUT almost 1/10". CIP law is .007" and SAAMI suggested headspace (usually American Standard) is .006, or visa-vis.
.097" headspace is excessively DANGEROUS.
That some people get away with just necking up 7x57 or 8x57 to hold a .375 dia. bullet and firing it, just proves the existence of guardian angels in my MOST humble opinion.
What will happen if those cases don't separate on firing, is that they are stretched in the web and will separate at some time in the future.
Even .019" headspace which is excessive headspace by .011" or so will leave a bright ring around the case at the web.
If using 57mm brass from the smaller ctgs. the ctg. must be necked straight before necking down in a 9.5x56/7 die.
This can be done easily with a .44 Mag or .45 Colt RCBS expander die. The nose of the expander needs to be ground on an angle that will enter the mouth of the 'parent' case.
I found it easier to make a new expander "plug" with more taper and do the expansion to 9.5 in one pass on new brass. Older, fired brass should be partially annealed first, yet when doing this on some old .30/06 brass for my .375/06IMP, I lost only 4 or 5 cases out of 50 old, oft fired .30/06 cases.