You'll prolly find TB is a little too bulky for seating full wadcutters in a 357mag or 38spl.
IMO, H-Clays is more suited for that application. A very similar powder from the same manufacturer, very close burn rates, only a less bulkier form.
I've been using 2.5gr-3.0gr in 38/357mag 148gr/158gr lead target loads for many years, with excellent results.