I used to get a lot of case-head separations with one particular rifle (a beautiful commercial long Lee). Often they split on the 2nd or 3rd reload, always about 1 cm up from the rim. Neck-resized rounds only fitted this rifle, so I had to segregate my brass which is a headache. I cured the problem by
(1) avoiding buying S&B ammo or reloading S&B cases (switched to Prvi, though I find HXP equally suitable, thick brass)
(2) selling the rifle
All 5 of my .303s now have similar chambers so I neck resize and don't segregate the brass. I just check that the rounds fit the rifle before I go shooting.
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