Sinclair #40B 40° Bump Gauge Insert, (25 to 338 Calibre) 257 Roberts Ackley Imp., 280 Rem Ackley Imp.
Sinclair Bump Gage Inserts are used to measure the amount of shoulder bump when setting up full length sizing dies. These Bump Gauges install in either of the Sinclair or Hornady comparator bodies and are machined to fit particular shoulder angles of cartridges. Rather than measuring to the datum line, these gauges indicate off of the shoulder of the case to get a better, more easily assessable measurement of how much you are actually sizing your cases.
Sinclair usually recommend between .001" to .002" bump for bolt action rifles and between .003" and .005" for AR-15 type rifles. Also, a useful tool for keeping your brass and loaded ammunition separated if you have multiple rifles chambered for the same cartridge and checking loaded ammunition.
Suitable for the following Cartridges:
257 Ackley Improved
280 Ackley Improved
257 Roberts Ackley Improved
260 Ackley Improved
257 Roberts +P Ackley Improved
25-3000 Ackley Improved
338-06 Ackley Improved
25 Ackley Krag Short Improved