I agree with the above, however, just recently using brass I have ALWAYS used, I ran into a problem that is a first for me. I am using NEW blue bag Winchester cases in 300WM.
I developed my loads in summer, so using the same load and once fired brass in winter SHOULD pose no problem...... not so I found out.
The very first shot at a pig had me struggling to open the bolt, so the mob of pigs were able to escape further destruction.
Upon opening the bolt, the case was very scuffed on the case head, the primer was VERY flat and there was a very pronounced ejector mark.
Now, prior to heading out, I ran a dry patch through the barrel to remove any oil or 'stuff' left over from cleaning it, so that couldn't have been the problem. So I decided to fire another round just to be sure it was in fact a load problem, not a gun problem. That case was also difficult to open, after opening the bolt with the rifle between my legs, the case came out less a primer....... not good me thinks.
When I returned home, I pulled a random round and weighed the charge, it was exactly what it should have been, within +/- .1gr of 81gr.
I am still perplexed by this, as the cases that were unfired showed no signs of excessive pressure, velocity or ANY other issue.
I do realise that new brass takes some pressure away during expanding to the chamber, but this would indicate it is WAY over normal pressure ranges.
Anyway, thought this may be interesting.
Cheers.