I recently started a new project in building the Triple R repeater machine gun from Bioshock Infinite. I have had several questions on how I did the spacing for the holes in the heat shroud. First thing I did with the tube for the shroud was to make sure the ends were squared off, so that when I stood it on a level surface, it would make a right angle with an L square. Next I took a piece of paper that would wrap around the tube and have both ends just meet, and folded it to make eight evenly spaced folds, I used that to make eight marks around the diameter of the tube. Using those 8 marks and the L square, I made 8 lines along the length of the tube for the 8 rows of vent holes to be cut out with the hole saw. Once I measured out the spacing between the holes along the lines, I used a little plastic cap with a hole in the center of it to draw the pattern on the tube. Lastly I just cut the holes and cleaned them up ! HERE ARE SOME PICS !