The RCBS Precision Mic for 7mm Remington Magnum is an essential reloading tool that enables precise measurement of chamber headspace and bullet seating depth to 0.001 inch accuracy. This precision instrument measures from the datum point on the case shoulder to the base providing spot-on SAAMI tolerance readings.RCBS Precision Mic - 7mm Remington MagnumMeasures chamber headspace and bullet seating depth to 0.001-inch precisionDatum point measurement system for accurate SAAMI tolerance readingsSimple operation with just a few twistsExtends rifle brass life through precise measurementsAn indispensable tool for serious reloaders who demand safe accurate loads and want to maximize the longevity of their rifle brass through precise measurements and optimal cartridge dimensions.