Hey Martin...Welcome!
Cratering is more a visual annoyance than anything else. If they were blanking (perforating), well, that would be a problem.
If you want to fix it, take a close look at the firing pin tip. From the factory you see they're ground on somewhat of a taper. Since when firing a round the primer stops the pin forward travel at about .020" protrusion the taper allows a bit of a gap between the pin and the pin hole for the primer cup to enter...craters!
By reshaping the tip to a radius, about .020" is good, the full diameter of the pin remains in the hole and eliminates 90% of cratering problems as long as they're caused by other problems, over loading and etc.
You may also find a bit of a chamfer on the edge of the in hole in the bolt face. That can also contribute to some cratering, but requires taking a facing cut across the bolt face or a more radical approach, rebushing the pin hole. For now I'd reshape the pin tip and go from there.
Bill
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