I have a 1913 Mauser sporting rifle (called a model B by the person who sold it to me a few years ago). I was able to find a couple of packets of Woodleigh 200 gn Weldcore in .318. They are accurate and would be perfect for Whitetail. I also have a reducing die made by CH tool and die. It reduces .323 projectiles to .319. And they work fine as well .
I have the Woodleigh loading book and it has load data for .318 Mausers. I can provide some loading data from it in a couple of days when I get home.