Sinclair bump gauge inserts are designed to measure the shoulder bump when configuring full-length sizing dies. These bump gauges can be installed in either of our comparator bodies and are precisely machined to accommodate specific shoulder angles of cartridges. Instead of measuring to the datum line, these gauges provide an indication from the shoulder of the case, offering a more accurate and easily accessible measurement of the extent to which you are sizing your cases. We typically recommend a shoulder bump of 0.001 inches - 0.002 inches for bolt-action rifles and 0.003 inches - 0.005 inches for AR-15 type rifles. Additionally, this tool is useful for organizing your brass and loaded ammunition, especially if you have multiple rifles chambered for the same cartridge and for verifying loaded ammunition.