I shoot a CVA Accura V2 50cal 1:28" with 70gr BH209 or 80gr T7 ff , both powder loads are great. I use a 54cal felt wad and a 460gr Bull Shop cast lead bullet. I would love to try the 395gr GP bullet like Mr. Lewis cast also.
You might want to look at this bullet made by Bull Shop... Dan sizes them to your request and uses a great Lube. His NASA Green lube really is good.
Here is a pic of the bullet recovered from an elk shot at 180-85 yards.
It is a .503x400 LGP (Lyman Great Plains). We use a MMP sub-bridge under the bullet to seal all the gas, and you can see the impression left in the base of the bullet.