My pick is 'other'

I'm not particularly worried about OSR as I don't need ultra-hard bullets and I don't hunt in no-lead zones.
If I were pressed to have only lead-free hunting zones to choose from I'd start the path down OSR-free/lead-free bullet design.

I don't own a nitro double rifle.
As yet I don't know of anyone speaking up on unleaded bullets for black powder bore rifles and black powder express rifles (with pre-nitro era steel and damascus barrels)

There would have to be some kind of definite 'other' solution for safe and consistent running in the pre-nitro rifles that would work out for regulation loads in my rifles.

I'm happy to listen to good answers to the pre-nitro double rifle 'unleaded question'

Cheers
Tinker