How deep is the rifling? What type patch will you use? What is the actual bore size?

I've used a bore sized ball, and one that is .005" under bore size. Both work well, but I get fewer fliers from the undersized ball because the patches come out looking better.

The amount of chamfer on the muzzle crown will make a difference also. Some shooters use an oversize ball, but I've found the muzzle must be chamfered well or the patch will be damaged when loading.

You may need to try a couple different ball sizes. You can get pre cast balls from TOTW.