I just fired one of the terrifyingly old, green with verdigris reloads into a log & the neck ID measured .3586
To say I'm thrilled by this & all of the history provided & discovered is a HUGE understatement.
I've never owned a rifle with this history or provenance before & to think that I'll actually be adding to its story is thrilling to me!
I will be hunting with it this year in my adopted home of Tennessee (I moved here from England, 11 years ago) and in Wyoming. I hope I can do the old girl proud.

Thank you to everyone for all the help, advice, tips & pointers. I can't believe I never discovered this forum before now!