Re: 30-378 caselife?
I did about the same as you 4 firings neck sizing only, full lengthed the fifth with a standard rcbs die. Back to neck sizing now. Starting to lose some from primer pockets. As I'm priming cases the very easy to prime brass gets a magic marker across the head, meaning.... Last Fire.
I'm about to take one case, back the load down a hair, reload, full length resizing it, checking for thinning ahead of the web, repeat until I see something I don't like. I just lost a whole pile of 5 times fired/ last 3 times FL sized match 300 Wby brass due to case head sep/thin. I thought full length sizing every time would be more consistent, well maybe if I set the dang thing up right.
That said my 30-378 cases have lived longer than my 300 Wby and I'm a bit harder on them too. But it is my own fault and not the brasses.
I couldn't see it by eye after the 2nd FLS but I have since measured some and they were 5-7 thousandths thinner just in front of the web. Now with a noticeable shiny line they are 15 thou thinner just in front of the web.
I also switched to a slightly faster powder for the last 2 firings....from RL25 to RL22. Similar vel, no marks. You think that could that be part of the problem?