Just don't cone too deep. IMO these tools have to shallow an angle.
I have a couple I have made and use carefully. But this is a better crown IMO. Bore is a little fouled from too much powder (proof load) but light and fouling combined to show the crown perfectly.

The relief cut on the lands was made with a tool like this. This is a 2 angle job on a friends hunting rifle. The outer angle was final polished with the wet or dry paper on the thumb trick. I really would try this before coning.

This is for larger bores but I recently re-cut it (again) and made a pilot to do a 50 caliber. Shown here it was for a .67. The 50 crowns were done first with a counter sink and a hand turned "brace" to break the edge of the lands then the tool shown with light pressure and my cordless 1/2 drill. It loads a .495 ball and a .018 patch with just rod pressure. Recovered patches are perfect.
I double stick tape wet or dry paper to it starting with 150 grit ending with 400 or finer.

Dan