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 a more accurate and easily accessible measurement by referencing the shoulder of the case, allowing you to determine the exact amount of sizing applied to 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, these gauges are useful for organizing your brass and loaded ammunition, especially if you have multiple rifles chambered for the same cartridge and for verifying loaded ammunition.