1886 in 40-65

[loophole]

I have sent a Winchester 1886 in 40-65 to Dennis Olsen to have a liner installed and the metal refinished. I have a Shiloh in 40-65 and have dies and a few hundred cases, and I love the caliber.
I asked Dennis to install a liner with 1:18 twist and .400/.408 lands and groves with chamber as close as possible to Shiloh.
I understand that the original Winchester used a slower twist, a .406 barrel and 265 gr. bullets. I think the action will cycle rounds loaded with 300 or maybe even 350 gr bullets and I would like to use them in the rifle.
Does anyone have any experience with a levergun with modern chamber and barrel dimensions for this caliber? any suggestions on a mold to throw a .310" bullet?
Thanks
Loophole