Those chamber checkers are hit or misses. You need to fire some cases from your rifles and use the RCBS Mic or the Hornady mic to measure the brass and set your dies.
Or you can keep on screwing down your die until the cases stops sticking in all of your rifles.
Problem with this is you don't know if you have overdone it until you fire the rounds.
Simple check for head clearance or the air space between the rear of the case and the bolt face.
1. Full length resize a case and measure the length of the case and write it down.
2. Using a fired spent primer take the primer and start the primer into the primer pocket just seating it enough to keep it from falling out.
3. Now chamber this "empty" test cartridge and let the bolt seat the primer making sure the bolt is fully closed.
4. Eject the case and measure the case again and write it down.
5 Now subtract the first case measurement from the second case measurement and this will be your head clearance.
Your head clearance will be the amount that you bumped the shoulder back, if its less than .002 you will need to bump the shoulder back further when resizing your AR15 cases.
NOTE: On gas operated rifle the majority of them are "over gassed" to ensure reliable functioning with low powered ammunition. The problem with this is the bolt can move to the rear while the case is still gripping the chamber walls. When the case releases it grip from the chamber walls there still can be chamber pressure in the bore. This chamber pressure and with the bolt moving to the rear can cause the shoulder of the case to move forward "and make the case longer than the chamber" and give a false reading on case length. This is where the spent primer trick in the primer pocket will give you a better case reading on head clearance.
Warning, the worst headspace you can ever encounter will be found in dimly lit bars and is caused by unscrupulous bartenders.
Edited by bigedp51, 08 August 2013 - 04:57 PM.