Just look into the European CIP max case dimensions. The bases and rims are different.
7x57R: rim diam 13.5 mm, rim thickness 1.60 mm, base 12.05 mm
6.5x57R: rd 13.32 mm, rt 1.40 mm, base 11.92 mm
So the 6.5x57R can usually not be easily formed from 7x57R brass. You better start with
8x57IRS brass. This one shares the base and rim dimensions with the 6.5x57R.