Refer to the standard formula from post #6 above which establishes a starting load of 70% of max, where a max load is the amount of TB as filled to the base of the bullet after it is seated. And the bullet weight makes no difference. A max load with any bullet weight will be mild, and if you start with the 70% load, it may seem that you are wasting your effort doing so--but do that anyway and then work up. And then for your next caliber, you may want to start higher and perhaps not even bother to weigh the charge as you become more experienced with using it.
For some time there was an admonishment going around that TB should not be compressed above the max loading and it was assumed by most that it would be dangerous to do so. But finally Hodgdon came across and acknowledged that the reason was not a dangerous overload, but rather might cause a dropoff in accuracy.
I load a .45-70 360 gr cast bullet to max and up to 10 or so additional calibers up to .416s and .458s which makes these comfortable to shoot rather than standing around gathering dust. In every case I start with a max load and not bothering to weigh it. Probably this max loading formula will leave some doubt until you have used TB for a while. Trail Boss has finally become more available in my area where it once was very difficult to find.
Trail Boss may be indicated as either IMR or Hodgdon but currently as I recall it is solely distributed by Hodgdon, but originally developed for IMR.
