No one has posted in this thread for awhile, but recently made the HiVis front sight change and I am very pleased with the results. Amazon carries the sight. To answer the question on the HiVis post shape, it is an oblong like the Sigma hole only a little too large. I basically just had to gently file the sides of the new post to cut it down to fit. I tried to take the same amount of material from each side. I also found that it was necessary to round the oblong edges slightly. When it finally fit it was snug with no play at all. I also used Blue Locktite. If you need to remove it in the future it will release with heat as from a soldering gun. Buy your self a small file. Mine is flat and about 3" long and very fine. Go slow and you'll be fine.