The list I have is for a .693" ball (true 14 bore) to be 500gr. in pure lead by formula. My new 15 bore Tanner mold casts a bit undersize at 6gr. under 15 bore size- no problem.

As I achieved only 1,550fps with 191gr. in my 12 bore shotoing a .684" ball, I suspect you'll make close to that speed only with Swiss powder. Just speculation.