It is very easy to determine if you have moved the shoulder back for your AR. After you size a few and get your die adjusted for the shoulder setback you want:
- wipe off the case lube from a sized case
- move the takedown pin to allow the upper to rotate open on your AR
- slide the BCG back
- slide the sized cartridge into the chamber
- the bolt should slide forward and lock with light to medium finger pressure on the back of the BCG
If it passes this test, it will chamber just fine during normal firing.