I made a chamber cast and found to my dismay that the chamber had been "polished" out much like the bore. Half of the chamber is nearly parallel, and there is one spot behind the neck that is so polished that it is wider than the case behind it.

My earlier measurements were off as the case didn't expand concentrically, probably due to the low pressures.

I had some time getting the chamber cast out.

Fired a light load again but with the same gas flow past issue and a sooty side of the case.

I may actually try an 8mm 06 reamer to see it that cleans things up. I could just have it rebored to .358 and turn it into a Whelen. Too bad that the body taper on the 9x57 is the same as the 8 or that would have been a perfect solution.