Looks pretty good - I made a pair of dishers out of those handheld sledges, myself. The trick to getting good spherical faces is to make yourself a paper template. Just draw a circle of your desired radius on a piece of posterboard, and cut it out. Then cut the piece of paper in half, so that you have a piece of paper with half a circle cut out of one side, like you took a bite out of it.
As you grind your hammer head, you can check it with your paper gage, and remove material as needed.
Steve
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