There is a bumper on the end of the buffer, maybe it compresses some. Could also be carrier tilt allowing contact, not sure but it sure looks like the dings I had on mine, I used an Aero tube as well and they are known for this issue. I notched my tube to get more threads engaged and secure the detent better as well, it was just captured by the tube and was leaning at an angle till I cut the notch for it.