dented cases

[Rocky Raab]

That happens after firing and not during resizing?

Some rifles ejecet the empty with enough force that the neck or shoulder area hits the receiver hard enough to dent it. If it's always in the same place and of the same depth, that's likely it.

Small dents won't hurt anything, although I'd expect you to see a crack there after several firings due to the flexing of the metal. If the shoulder is deeply dented, that case is toast.