I have a unique AR15 barrel, it's a 10.5 inch 6.8 spc. There were only 4 made by the manufacturer and they had undersized gas ports. I need to open it up from .075 ish to .086. Now I have the bit and was thinking I should fixture it up in my drill press but was considering putting a sub caliber brass rod in the bore to prevent hitting the far side. That way when I am peck drilling If I see brass shavings I know I am through. Sound like a plan or how would you do it?