This issue of chamber length standardization to 70mm is hard to nail. In fact, we are still trying to figure it out for 12 bore in American guns. Some say late 20s and some early to mid 30s, but who really knows?
By buying from RST or Polywad you're not 'Hamburgerizing' which needless to say is at this time. My suggestion would be Aguila 1 oz load with Vo of 1200ft/sec. Not 100% sure, but I think each box has CIP monogram.