You can smoke the case shoulders by passing them through the tip of the flame of a butane lighter, or a candle flame. A very light coat of oil on the brass (wipe it with an oily patch, then dry it with a dry patch) will help to gather the soot from the flame.

I'd work on backing the die off in 1/4 turn increments until the contact area is close to that of the factory round. Then you can fiddle with getting it exactly right--and lock the die lock ring so it doesn't move!