prairie ghost'
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When trying to make cases with the correct headstamp, if you take the original headstamp off and deepen the primer pocket (with primer pocket uniformer) before establishing the headspace by fireforming, it shouldn't cause a problem. For belted cartridges, you should set the dies up to headspace on the shoulder. In my experience, removing about .015" will take the original headstamp off. Removing less than this may be enough to make the original headstamp inconspicuous.
Mike