I sure don't hit a gopher on every try Doc. According to the tight little 2 inch groups it shoots on paper from a good rest, at 25 yards, the misses are my fault though, not the revolver.
If you can push .375 balls with your thumb, you will need those .380 balls for sure. The mold I use to cast mine are marked .375, but I have never miked a ball, so they could be a little larger than the mold mark. The recoil with 15 grains of fff is almost non existant in mine, so I doubt you will have problems with the .375 ball moving in other chambers, but I suggest using plenty of lube over the ball to guard against flash over.
I use Gatofeo's lube recipe and wads cut from felt weather stripping under the ball. As he points out, they make for a pretty clean bore, even after many shots are fired. Just one of the several helpful hints he has provided this board with.
I would bet I am at least as dangerous with a Dremel, as you or anyone else. I have learned to wrap the work piece in several layers of cloth, and lock it in my rubber padded bench vice. Then I can support the Dremel with both hands, while my left forearm is resting on the jaws of the vice. After learning this, I no longer cut unwanted designs on things. Because I'm not partial to V notches, I just cut sraight down into the notch. Easy does it, and when you see you have removed a small amount of metal, stop grinding, load one chamber, and try it. Each time , the point of impact will keep droping. Repeat until you reach point of aim. I have "regulated" the sight notch on all five of my Colt style Italians, and the slit in the hammer does not appear to affect the hammers ability to capture cap fragments.
I don't know if the heigth of the front site would correspond with the amount removed from the hammer or not. Logic says it would, however, I have a friend who didn't want to alter the hammer on his several Colt style revolvers, so he made taller front sights from brass brazing rod. To my eye, his front sights look taller than the distance I cut into my hammers ? I would strongly suggest the careful, "little at a time" approach, rather than trying to find a formula, and removing it all at once.