Question about uneven wear on bolt's lug faces

[SDW]

So... I got that tool turned down to the correct size for a snug fit in the upper receiver, which after some reflection I now recall to be an Aero Precision upper receiver. Overall I think this job was worth the effort. After about 15-30 seconds of spinning it in the drill with 200-grit paste, I inspected the Upper's face and saw that a section of bright metal had appeared, centered at about the 4 oclock position. So more spinning and checking made that bright metal surface grow to half and then finally about 80% of the circumference. I figured that'd do the job. Didn't want to go nuts with it.

I have a couple of other uppers, 5.56s, that I want to hit with this tool at some point.