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Sinclair Bump Gage Inserts are designed to determine the extent to which the shoulder needs to be bumped when configuring full length sizing dies. These inserts can be fitted into either of our comparator bodies and are machined to conform to the specific shoulder angles of various cartridges. Instead of measuring up to the datum line, these gages read off the shoulder of the cartridge to provide a more accurate and easily accessible reading of the degree to which the cases are being sized. Bolt action rifles generally require a bump between .001" and .002", while AR-15 rifles require between .003" and .005". In addition, this tool can be used to identify and keep separate your brass and loaded ammunition if you have different rifles chambered for the same cartridge. Furthermore, it can be used to check loaded ammunition.