So you have ~100 rnds. through it now. What does it do when you fire the last round in the mag? Does the bolt hold open? I have a hard time believing that a follower would survive that last shot if it was snagging the BCG/Bolt. Look at the BHO. Does it show signs of wear/damage on the chamber side?

How about post a pic of the BHO with and without an empty mag inserted (upper off, of course).