Had the hmr for a good few years now but is not used as often as some are, so haven't put thousands of rounds through it.
Tried different ammo brands as you do, and checked every round with a magnifying glass and usually got 2 to 6 cracked cases per box. Way too much.
After a clean, I was doing a re-zero and had my first stuck bullet head. I was wearing a pair of Napier pro 9 ear protection, and heard a click rather than the normal sound expected. Removing the case, the powder was compressed to the end of the case with the case being split.
The bullet head was only in a little way, so if I had tried to I would not have been able to load again. Reluctantly I tapped it out with a Dewey rod, but it came out quite easily.
This was an old batch of ammo which had been checked and had deteriorated since checking, the batch code was stamped on the bottom of the label. My new batch is printed in big lettering on the case. Hopefully this new batch will be of better quality.
SO, is there anything that can be carried with you in the field should this problem re-occur ?