Could be work hardened brass if the chamber is OK. After checking the chamber I would try annealing the cases to see if this helps. For a single shot not much neck tension is needed so you could back the dies out and size less possibly. If you have an over sized chamber and or under sized dies ether sending them back to the manufacturer or polishing them yourself could help.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli