In my experience i have only ever had issues with federal casings splitting. I haven't shot 270wsm but a 300winmag i had seen the casing split or bulge and had slight issues removing the casing. Another thought is that the bullet is not perfectly seated when the bolt is closed and the recoil is actually moving the casing back into the bolt? Have you had the same issue with different manufactured ammo? I am sure there are a number of different possibilities.
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