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.
When using this method I found that I have to use a lot of finger pressure to chamber any of my resized rounds and even new rounds. What does this tell you? I can feel the way it should feel when I close the bolt with no round in the chamber. What should I do to find out why it is "stiffer" than it should be? Btw, I have not had any malfunctions occur at all with new ammo and have not fired any reloads yet.