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Can you try one factory cartridge and see if the same thing happens?
If you don’t figure it out and you get the gun back….mark the case with a sharpie and index the mark 12oclock in the chamber. Then see where the dimple is in relation to your indexed round. Do this with a couple rounds and see if it occurred in the exact same spot. Then you have a map and starting point that could help identify the problem.
Is there usually black soot in the dimple? It looks like the neck didnt seal in the chamber and gas blew back and made it. Ive seen it from light underpressure loads.