Solved.. the bushing dies only resize the top 80-85% of the neck, and although the rounds easily chambered, gauged correctly, etc, they hung up just enough for cases with defective rims to rip the rim off. I expect that a rifle gas system (versus carbine) might have been gentle enough to not have the problem.
Where the rim groove was cut, there must have been a burr on the cutter causing it to actually undercut the groove towards the rear of the case, effectively reducing the strength of the rim. These are NOT extractor marks, the undercut runs around the rim, perhaps as much as 1/2 way.
Went thru 2,000 cases and found just a handful of cases like this.
End result, sized further down the neck (.025"), no load change (it's only paper), 250 round test fire.. zero issues, and zero bits of brass on the bolt, no swiping marks on brass...
Thks for the suggestions \ help!
Where the rim groove was cut, there must have been a burr on the cutter causing it to actually undercut the groove towards the rear of the case, effectively reducing the strength of the rim. These are NOT extractor marks, the undercut runs around the rim, perhaps as much as 1/2 way.
Went thru 2,000 cases and found just a handful of cases like this.
End result, sized further down the neck (.025"), no load change (it's only paper), 250 round test fire.. zero issues, and zero bits of brass on the bolt, no swiping marks on brass...
Thks for the suggestions \ help!
