I have a bunch of GI 7.62x51 leftover from my failed attempt to make some money swaging it down to 6.5 Japanese.  Even took out an ad in American Rifleman.  Then companies other than Norma, who made the very undersized stuff that failed early, started making the brass and I lost my market.  It was too much work anyway.  But, the Niemiller is the .243 with its shoulder pushed back .1".  Enough to prevent chambering the .243.  So the Niemiller could be made from any .308 based case.