Fairly normal for older rifles. Generous chamber, combined with the brass being relatively thick at the base. The case fireformed to the generous chamber. The base, being thicker and supported by the rim etc, does not expand as much. It’s also why the case wall is scuffed and the base is shiny, the wall is contacting the chamber and scuffing, the base does not, so remains shiny.
It probably expands on firing, at the base, but not enough to fireform it.
Edit: as far as a remedy, none really, beyond a new barrel or rechamber. Different brass will produce different results, some may be worse , some better depending on how thick the brass is and how it’s drawn during manafacture.
Case life, probably shortened slightly. I would not be overly concerned.