I experienced a similar issue with center fire ammunition from Remington a few years ago. I was sighting in my Dads 270 . I fired three rounds for POI and made a scope adjustment. On the next shot the bolt was very hard to open and the primer pocket was enlarged. Never having had an issue with factory ammo I fired another shot. The bolt had to be opened with several hard blows with the heal of the hand. The primer was gone and the case head was shaped to fit the bolt face of the pre 64. I did not continue shooting and had the gun checked by a smith, no issues with the bolt were found. I sent the rest of the box to Remington and their finding was that the lot of ammo was 20 years old, although it had been recently purchased. Their conclusion was that the bullet jacket had bonded to the case and the powder had started to degrade, probably due to storage issues. I don't know if this could have happened to your HNR ammo but it is one possibility.
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