Does it shoot good?
Checking the bore would be the next step I would take. If no carbon build up in throat and first few inches of barrel then inspection of bore for diameter is needed.
Sounds like size die is not sizing brass enough? If case cannot expand at all this will make pressure higher ... expanding case act like a shock absorber ...same as water on rnd or in chamber causes an over pressure condition on upper end loads.
Hammers with 4166 at 2975 and RL 16 (slow, but I haven’t done much load dev).
The sizing die works fine for the 4166 and Rl16 cases.
The barrel shoots great with other powders no complaints, I just wanted to find a way to make varget work because I have a lot of it. After hearing the loads/velocity everyone is getting here, it’s making me scratch my head. Maybe I have a hot lot of Varget.