Just bought a brand new M&P AR and took it to the range and ran 150rnds down range without a hiccup and it was spot on at 100yds after making a few adjustments with the iron sights. After taking it apart to clean I noticed that the grease mark pattern on the bolt wear was only half the width of the hammer and noticed a small burr on the top of the hammer. Question is should I leave it alone or take it off and if so what grit sandpaper should I use? Thanks in advance for any help- ken