You should try .530 and .535 balls with patch material from .010 to .020 and let the rifle show you what it is going to shoot best. There's no way to predict what your barrel is going to respond to. Approach it as you would develop a hand load, the rifle will show you what it needs.

"The only thing necessary for the triumph of evil is for good men to do nothing."
Edmund Burke 1795

"Give me liberty or give me death"
Patrick Henry 1775