I've used Trail Boss in 38 spl with 158 gr SWC's. It is a great cap gun load. What T.B. told me was the max load for 460 S&W mag was to the base of the seated bullet. Do not compress. Minimum load was to reduce 70%. It didn't matter what bullet. On My 460, I have tried 200 gr LRN, 250 gr JHP, 300 gr LRN, and 300 gr JHP with T.B. using that formula, but usually at the upper end. Perhaps 90% loads.

That big doughnut flake meters better than unique. You will end up with less weight than Unique, but more volume. What I'm saying is... You will back off your powder measure screw with T.B. vs. unique.