Jeff - if going the .505 Barnes Supreme,there is already loading data out there for starters.
A fellow in Vancouver, B.C. made one up in the 70's and I got to shoot it. Wish I hadn't. 600gr. bullet at 2,600fps. That hurt. I think it used the full length .460 Weatherby case and was built on a .602 Brno action. I bought the unfired .375 barrel from the guy. No mention was made of any difficulty getting the action to feed.