Hi Grant - yes, the .395" ball will work just fine. If you were involved in bench-rest shooting, then bore sized or every larger balls are normally
used, with teflon coated patching & religious-grade wiping between shots. The larger balls and tighter loads do give increased accuracy, but at
a price and level not normally needed for general 'work'.
The muzzle's crown is vitally important in easing the loading. The short radius we put on our muzzle crowns, is the correct angling needed for
moving metal. The metal being moved, is the lead in the ball and the smoothness of the crown's corners, is necessary to prevent over stressing
or cutting the patch material.
Indeed, the angles we use are also used by Corbin Mfg. in making their jacketed bullet making dies. I researched this 'phenomenon' many years
ago and replicated it in the "muzzle crowning" we now recommend.