Ok, little more info on my original 12 stop Richards cylinder. The walls between the chambers are .031" at the cartridge insertion end (top) and .0465 at the bullet exit end (bottom). The wall thickness to the exterior of the cylinder is .037" at the top and .083" at the bottom. I'll try to redo all the measurements this weekend as I now have a better caliper.
And a little more to add, apparently the depth of the locking notches is around .033", leaving barely .004" of steel, 1860s era steel, to contain the cartridge case. No wonder so many of the converted cylinders are found with blown out notches. I wonder if the replacement cylinders had notches that were any shallower or if that area of the new cylinders was made thicker? Anyone got one they can measure at some point?