I posted one in the last discussion about this, showing that the caps are NOT cut dead center. And no two cases seem to be exactly the same. I know people got all upset and argumentative, but I pointed it out because I had the SAME idea about going from the flat cap surface, until I did some measuring. It can get you close, but it's faster for me to use the proper tools, and I do it for a living, so speed and accuracy are paramount, but at the end of the day, your pattern is what will be the final say. Hope this helps clarify.