There is plenty of proven load data for the 173 grain Keith SWC bullet in the Lyman cast bullet manuals, including the latest one. PM me if you want some specific data and don't have the book.

Personally, I used to use that bullet for heavy 38 Special loads, but there are well known problems (and solutions) for when used in .357 Magnum ammo. So, now I stick with 158/160 grain bullets in both cases and am happy.