Stimpy is no beginning handloader, so I'm certain he used rifle primers. Also, when he says a moderate load of 4895 I believe him - excessive pressure is not likely due to a "fast" lot or just 20F more temp. Case setback due to a too-smooth chamber could cause sticky extraction or a flattened primer, but not primer flow into the pin hole. High pressure is the most likely cause.
Severe fouling of the bore can raise pressures, but not too likely here. It could be a matter of him never loading up to normal high pressures before in this rifle. I once had a Handi that had a too large firing pin hole, but at moderate load levels the pin indent looked fine. At max load levels - not excessive, just hotter than moderate - the primers exhibited flow into the hole. Perhaps this is the answer, although only Stimpy will know.
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