I form my 9.5x57M-Sch aka .375 rimless NE cases from W-W or S&B 30-06 brass, trimmed to 57mm of course. Merely necking up 8x57 or 9.3x57 brass led to problems from excessive headspace. For more on my rifle and load see:
http://forums.nitroexpress.com/showflat.php?Cat=0&Number=173003&page=0&fpart=1&vc=1