Question...what do you want to accomplish with this new barrel? Yes, the 460 will shoot flatter, but if you want a flat shooter, why wouldn't you just buy a barrel in a pure rifle cartridge? I mean, hey the .280Rem is a whole lot flatter than any 460. If you want to chuck big lead, I would think the .45-70 would make the most sense...easy to find ammo, loading components, and it won't kill your wallet in the process.
Jim