Matt,
Interesting information on the 1910 & 1915 dimensions. I wonder if this was done primarily for battle rifles where a loose fit might compensate for debris on the ammo or in the action? Would be worth it to see readable period engineering drawings of this.

Just to add one more variable: the “.256 Fraser Flanged” (simply the 6.5x53R case loaded with the Fraser bullet) was spec’d at a .069” min/.070” max rim thickness.
- Mike