This is just a FWIW thread as I may have posted this earlier. I was priming some 9mm mixed brass yesterday and I had one that had an undersized primer pocket, not just tight but I smashed a primer attempting to seat it. I then remembered I had run into these before. IK 21 headstamp (Igman Zavod, Konjic, Yugoslavia). I was using my Pacific single stage with a ram prime so it was pretty easy to smash a primer. I went through a bunch of other brass and found 3 more (and I had chamfered the pocket mouth so I had run into this before). I didn't bother to measure the pocket diameter, I just tossed the remaining brass. Just another headstamp to look out for...