I was at the AGC today, and after running about 50 rounds through my AR9 the bolt key socket head cap screw broke and of course the gun would not cycle anymore. When I got home and disassembled the upper from the lower - pulled the BCG and saw the broken cap screw. I was a little surprised that there was only one screw holding the key in place, but now I need to extract the screw from the bolt without buggering the bolt threads. I have small screw extractors but what’s the best way to get a small bit to bite into that hardened screw without messing the bolt threads up?