I make gages, I start with measuring the length of the case from the head of the case to it’s shoulder. By whatever means I record the measurement, I then fire the case and measure the length of the case from the head of the case to it’s shoulder again, the difference in length of the two is the effect the chamber had on the case when fired. Autos and semi autos are said to be rough of the case when fired and extracted. If any part of the .008 thousands is being caused by the violent extraction the case will not chamber without resistance.
Again, I would suggest making an attempt to chamber the +.008 cases, I would then adjust the gap between bottom of the die and shell holder with a feeler gage starting with .005 thousands. After making the adjustment I would size a case and attempt chambering the case, if the case chambers I would increase the gap and size another case and attempt chambering, again I would continue increasing the gap until the case chambered with resistance.
I have bar dies for 300 Win Mag, 270 W and 30/06, I do not use them, but JIC, I have them JUST IN CASE.
My favorite cases are trashy old cases that have been fired in trashy old chambers, with my press, die, shell holder and the feeler gage I have 8 options when deciding the length of the case from the head of the case to it’s shoulder.