What Hatcher was referring to is what "could" happen if one was to experience a longitudinal split in the rear of case body. This was common with some FA34 brass, and I've used some 1950's Israeli .308 brass that had this problem (not in the type 99). As of 1947, hatcher had only seen one case of it with the 7.7, though he didn't say what year or manufacturer case it was. The difference in case head size is really no more than that of US vs European manufactured 6.5x55, where US made is some .008" smaller.