I think the concept of chamber adapters success more applies to shells using modern shot cup type wads. the base of the shot cup would not have that far to flair out from modern 10Ga to 8Bore ….. nominally .775' to .835" so .060" total divided by 2 is only .030" each side.

Traditional card & fibre, greased cloth, whatever wads might not be a good solution to the chamber adapter…..

- Mike