I just got a new upper and put it on a lower that  has about 2000 rounds on it. The new upper seems to be tearing up the buffer in the old lower. When I used the new upper the buffer got a circular pattern in it after about 150 rounds. Any ideas?



The bolt carrier from the new upper is the lighter colored one on the right, it looks like it has extra machine marks near the top of the slot.

The carrier feels smooth around the end that contacts the buffer. In the picture of the carriers there looks like theres an issue around the "channel" for the buffer detent, but it's smooth.

Edit: I have'nt seen machine marks like those on the carrier before, it is like that carrier was an M16 carrier that was machined to be legal.


EDIT: PROBLEM RESOLVED, IT WAS THE BOLT CARRIER.