With far and few short mag uppers with a larger than 308win case ejection ports, who has modded their own or bought a well quality control receiver? KAK is NOT that well for QC on uppers and lowers in my experience. I have 2 AP uppers coming next week (hopefully) to be Dremeled out. I care nothing about the use of the port cover if needing to enlarge the upper portion where the cover latches. Not sure at this point to know when is too much enlarged, but making sure not to get into the bcg raceway.