After tumbling some flash holes are blocked by a grain of the media. Some are jammed in fairly hard and increase the resistance for the pin which pushes the spent primer out. It may be overly cautious to avoid that. I handle the cases for inspection anyway so itīs no additional effort. I also hoped that tumbling might clean the primer pockets. It does not.
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If it isnīt broken, it doesnīt have enough features yet.