35Whelen,
PM a young fellow with the moniker of ASH he actually has one of these rare old birds.
I would reload first & see if the barrel was completely washed out, some rifling styles look rather shallow; but more than enough to stabilize the bullet!
You have a fantastic old girl there, a bit of TLC & she'll be up & going.
It would be best to slug your bore before buying projectiles as this calibre existed in a few guises.
Try & get Graeme Wright's Shooting the British Double rifle he has some good loads for it there for it.
Cheers
93x64mm