Here's one I have not seen before. I acquired some once-fired Barnes (Remington) .470 NE brass and the majority of them have approx. .280 circles "impressioned" into them just below the shoulder. Test chamber markings? Anyone with experience in this department? I don't see the marks as an issue, but curiosity has the best of me.

My limited brain says there has to be a mirror image in your chamber.

I'm looking forward to hearing what the experts feel it is because I have no clue as to what caused the mark in the chamber.

Fired in a pressure test barrel. The marks are from where the piezzo transducer sits

Thanks now I've learned something new today.

Suspicion confirmed, thanks Tailgunner.

Yep....pressure test barrel

Size them, shoot them and the rings should be gone after a few reloads!

You bought those as once fired I bet.
When those were fired for a pressure test they did not perforate to put pressure on the copper crusher.
I got (6) 375 H&H cases like that.

Most likely they will crack and leak in a shot or two. At least I never tried to use the ones I have.