The RCBS .243 Winchester Precision Mic 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 reloaders with spot-on SAAMI tolerance readings.RCBS .243 Winchester Precision MicDetermines chamber headspace and bullet seating depth to 0.001-inch precisionMeasures from datum point on case shoulder to baseProvides accurate SAAMI tolerance readingsEasy operation with just a few twistsAn indispensable tool for creating safe accurate loads while extending the life of your rifle brass. Perfect for precision reloaders who demand consistent reliable measurements for optimal cartridge performance.