This is from a Chapuis 9,3x74R double.

Chamber wall thickness is .260

Cannot measure the bbl till after the bbl block.

Then at 2.7 inches .776
scope mount in the way till
at 6" .772
at 8" .607
at 10" .566
at 12" .548
at 14" .532
at 16" .523
at 18" .516
from 20" to 23.5 .520 to .524.

The Chapuis 9,3 bbls are the thinnest of all the 9,3's I have seen.

The width at the breach face of both bbls is 1.829.

From the bbl flat to the top of the bbl is 1.09
Hope this helps.