This^^^^I don't know much about this cartridge but do you have to turn the necks on the brass and trim? Might be tight brass issue
With new brass that is not fireformed it is sized to fit all SAMMI chambers. So that means on the small size so it will fit even small chambers. When you fire new brass in a chamber it will take some of the pressure to push the brass out to fit your chamber. Next firing that energy will not be used to fireform the brass and and it will show as slightly over pressure. We are talking close to max loads here. If you are at starting loads you should not see pressure either way.I may have it backwards but I thought it was usually the other way around? After first firing and resizing closer to your actual chamber spec you had more room and may be able to bump up a touch?
I very well could be getting that mixed up with fireforming and loading for AI cartridges though, just wanted to check myself since I thought it was somewhat the same idea for both.
Full size and ^^^^^^^^^^^^^^^I'm with North Idaho. Measure your cases especially the shoulder.