I have come to the conclusion its inconsistent brass, nothing to do with cleaning or heat etc. I have gone through the same thing with my 7mm PRC. Managed to weed out most of the bad brass now it seems, i started with 3x packets of factory ammo & pulled it all to get the brass originally, Then another 2 packets after having to biff some of the original brass.
I shot a bunch of 175 ELDX over 2225 yesterday doing seating depths, below book max charge & experienced the same thing as the first lot of development i did with RL26. Every now and then a stiff bolt lift & stamped/swiped brass, sometimes last shot on a string sometimes first, no particular pattern. Primers all look the same & was all shot across the chronograph & the "hot" loads went no faster than the others. Clearly cant be heat related as sometimes it would be the first shot that would do it after a 10 min cool down, id follow up with 2 more straight away to complete the group & they would be the same speed but no stamp/swipe.
I think all you can really do is either run really slow/soft loads, or if your trying to run it fast/up close to max just throw out the bad brass & eventually you will end up with stuff thats ok.
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