I have seen this type of peening many times. It comes from many rounds being forced back onto a not so hard breech face. The raised area is a combination of the sunken primer pocket bearing less on the breech face and the firing pin forcing the rim of the hole out. This is not dangerous in its present state. The raised rim will not actuate a primer.
I have done what has already been suggested in the past, which is to hold the breech in a vice and pound down the raised area.
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