Quote: I seen something on another reloading sight THR saying that low pressure will also cause cratering.
Low pressure allows firing pin to drive case forward enough to push shoulder of case back which increases headspace slightly. Primer, which is then not held flush against bolt face, is driven back against bolt face, getting a running start and is flattened when it contacts bolt face. Primer will show same signs as high pressure. The "tophat" is a classic symptom of excessive headspace since primer walls are unsupported when primer driven back a few thousandths.
Regards,
hm
Low pressure allows firing pin to drive case forward enough to push shoulder of case back which increases headspace slightly. Primer, which is then not held flush against bolt face, is driven back against bolt face, getting a running start and is flattened when it contacts bolt face. Primer will show same signs as high pressure. The "tophat" is a classic symptom of excessive headspace since primer walls are unsupported when primer driven back a few thousandths.
Regards,
hm