Now you have it in a nut shell Jim. You can with a concave punch get enough pressure on a reloading press to cut 0.020 material, but the knock out is what you want to make the check out of and if it is not a near perfect circle with an evenly cut edge it will not form properly. I am never said you couldn't cut it with a reloading press, I said you couldn't cut it and have anything worth making a gas check out of. I just don't see any way around a flat bottom punch cutting out flat circular disks.
Even at the Sierra Plant all of their punches that punch jackets start out and maintain a flat bottom all the way through the drawing out process even on the boat tail bullet the punch has a flat bottom. Round does not work for bullet or boolit bases.
Best wishes from the Boer Ranch,
Joe