Low pressures????? Have you looked at Hogdon's data for TB in that 45/70? People seem to be making the VERY erroneous assumption that the low velocities automatically mean low pressures and that's simply not true for these big cases with Trail Boss! There are a bunch of loads listed there using other powders that have nearly twice the velocity for the same or even lower pressures, for example,
Trail Boss .458" 485 gr 804 FPS @ 23,300 CUP
vs
Benchmark .458" 485 gr 1503 FPS @ 23,400 CUP
or
IMR 4064 .458" 485 gr 1280 FPS @ 17,400 CUP
TB may be ok for pistol cases loaded to slingshot velocities but for these big rifle cases there are MUCH better choices for both velocity and low pressures!