From a recent batch of ADG 6CM, I drew a sample of ten cases. Their weight had an ES of 0.9 grains and SD of 0.37 grains (170.4 grain average weight).
I took two measurements from each neck, both the maximum thickness I could find and the minimum (so 20 total measurements). The ES of thickness for all 20 observations was 0.0009" and the SD was 0.00036".
I haven't tried Bertram.
My CM numbers pretty much mirror yours but the CM is a relatively light case compared to the magnums so they will have slightly more variance in weight. The necks I would expect to be the same.