Update here after many hours at the loading bench and range, trying to find a load for my S&W 10-5 that shoots to Point of Aim..
Below is a target shot with the best load: 3.7 grains Unique behind a Lyman 35863. That bullet is a 148-grain, double-ended, bevel-base wadcutter..
I never looked at Unique as a wadcutter powder, but won't complain about the results. Range 21 yards. Six o'clock hold. I take full credit for the flyer.
Other powders that showed promise but didn't group as well as Unique are Herco and HS-6.
Thanks for all your suggestions. In the final analysis I followed the advice of member gwpercle who suggested "Keep on experimenting."
Attachment 268039