As far as starting to load for a 180 grain bullet with a 200 grain load, I think that would be OK, You always use more powder with a lighter bullet, so You should be safe, as long as you start with a lower amount. I have seen various companies using drastically different powder amounts for the same bullet. THink it has something to do with the way the test barrel is throated.
I see what you are doing using the ball powder. I run out of room with my 180 grain bullets and IMR 4350. I too am trying to work up a good 180 grain accubound load with h 380, IMR 4350, W 760, Or Win 760. Good luck.
I used to re-load but now I "hand-load".
-- Well, at least I try