... I about max for that load in .38 special. The velocity should be just over 800 fps. Get your GF to shoot those and see how it feels. Since the 66 is .357 I'd go up until it gets uncomfortable.

I put Pachmehr and Hogue monogrips on my 'j' frames and I can shoot them hot without much discomfort at all.

The Alliant .357 table says that 6 grains of Unique will shoot a 158 gr swaged bullet at a little over 1000 fps.

I'd work up between 5 and 6 grains to get the load you want.
I'd just guess that about 5.5 grains of Unique would get around 900 fps so you can work from there.

I'd think that somewhere in that range you'll find your load. I don't think leading will be a problem at those velocities either.

I don't particularly agree that pin point accuracy is the most important factor in an SD gun because you aren't shooting bullseye. Reliably hitting the center of mass should do the trick.

You should have a load that you can get quick follow up shots with.

Forget 'FBI'. The max load is the one that you can shoot repeat shots with quickly and accurately.

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