measures .22 lr rims
rounds are placed in a hole and the gauge moved until it stops
once gauged the round is placed with others of the same mark
once batched, rounds have identical head-space and therefore be held in the breach in a identical position prior to firing - immediately improving each batches´ ballistic consistency
this critical process is necessary to improve scores by paying greater attention to the smallest detail - some times a simple rule even forgotten by the best
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