One thing you need to be aware of is that you should sort your brass according to head stamp. While these appear to be all WCC, some are NATO marked and some are just date stamped. Internal case volumes may vary between dates and manufacturers
You can check the weight of the case and see if there is any difference between the NATO marked and just the date marked cases. If there is, the volume may be smaller on the NATO brass.
The third case from the left of your second pic looks like a cupped firing pin indentation which would be indicative of high pressure. It is difficult to tell with a pic. Have you looked at them under magnification?
If this is happening with new factory ammo it's probably an anomaly with the new bolt and may go away after a few hundred rounds.