Datum is .400" Take a 40 S&W or 10MM brass. Remove the primer. Place 40 case mouth on fired 308 shoulder. Measure. Compare to sized.
This is my comparitor.
Datum is .400" Take a 40 S&W or 10MM brass. Remove the primer. Place 40 case mouth on fired 308 shoulder. Measure. Compare to sized.
This is my comparitor.
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