Found two yugo cases headstamped 12 / star / 53 / star and nny 1958-(cirillic letter) . Both are listed in the Yugo 7.9 mm ammo headstamp checklist by Phil Butler and others as ball loadings. What was the bullet like? A S.s. or a S. type?
Also, I am not sure that my steel sample ( nny 1958) was a ball loading since it is slightly shorter than the other ( 59,60 mm vs 56,95 mm) and the case mouth has a sort of slight “roll crimp”. It might be a dented mouth if the fired case hit the ground with its mouth after been ejected, but the crimp is rather uniform on the entire mouth
red stuff inside the mouth is rust, sorry for the low quality picture