I load for a 300 WSM
. I use redding bushing dies with Norma brass and neck size only. Haven't had too many issues.
It could be a shoulder issue. Soft brass might expand so much on the first firing that it is now hard to close the bolt on. Are the once fired cases hard to chamber before being neck sized?
Might be the firing and then resizing of the necks is stretching the neck and the neck is too long for the chamber. Should probably check the max cartridge length an make sure that it is not over after sizing the necks. Which brings up the question: Are you trimming the necks after the resize?