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The appearance of fired primers is a notoriously poor way to gauge pressure.
To expand on this, sometimes "overly-sizing" a case (too much shoulder bump) creates a gap between the cartridge and the boltface. The firing pin pushes the case forward and upon ignition, the primer backs out a little. As the case expands it squishes the primer giving the false appearance of excess pressure.

An additional downside of "oversizing" is the potential for case separation. A case gauge is a good tool but has limitations. In reality, you need to size cases in relation to your chamber.

 

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Cases were once fired military brass, they had to be sized twice to fit in my cartridge gauge
You need too run them through a 30.06 sizer FIRST, then run them again through your .308 sizer.
Long time ago when I first started reloading surplus brass an old timer at the range gave me that advice. Been doing that ever since.
 
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