I'd considered doing something similar with Nosler Partitions, forming a concave in the base sorta like a Minie Bullet.
BTW, does anyane know how the gain twist in a Carcano barrel starts out and ends up? Don't know how reliable the info I have is but it lists it as starting out at a rate of 1:19.25 at the breech end and finishing up at 1:8.25 an the muzzle and the rifling makes the same transition regardless of barrel lenght.