The best way I know to remove material to refurbish overly-thickened case neck walls is an inside case neck reamer. This is a Forster, designed to work with their case trimming base. Trick is knowing the case condition it was designed to be used with. This one is dimensioned for use on fired, unsized case necks (it’s 0.003 under bullet diameter). Run it on a sized neck and way too much brass comes off. Various sizes are available.
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