Since no one responded and said "you'll shoot your eye out kid" I went ahead and ordered some 1/4" and 3/16" ball endmills. I laid out the locations for the 6 flutes by wrapping a piece of 2" packing tape around the two steps so that it was square and the ends overlapped. I then cut through the overlap using a piece of angle iron as a guide. I now had two pieces of tape the length of the surface of the barrel. I placed the tape one at a time on a steel square and colored the tape with a marker. I measured the tape and diveded by six. Then using calipers I scratched off the marker lines to the corect spacing on the tape. Then I covered the tape with a longer piece of tape to protect the marker and placed it back on the barrel with the middle of one of the spaces centered on the gas port. I then milled out the slots and blasted the barrel so I can hopefully get it parkerized tomorrow.