I measured the primer pockets of several brands of 6.5x55 brass.

PMC once fired .525 mm
Igman once fired .524 mm
Lapua once fired .526 mm
Lapua new without primer .525-.526 mm

My caliper may be a thousandth or two off. Also, the readings I got varied by .001 depending on where I held the caliper in the primer pocket.
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