Trail Boss is a fairly new powder (5 or 6 years on the market). When I introduced my friend to reloading, I researched for good powders with which to teach the mechanics of loading. Something forgiving and voluminous. I settled on Trail Boss.
My friend was able to find only jacketed bullets for his 500 S&W and had 400 of them and nothing else. (A shortage at the time)
When I didn't find any load data for jacketed bullets, I contacted the maker. They replied "Trail Boss does not like jacketed bullets". I was disappointed. Not only because we could not load anything but also with the scanty answer.
I emailed back, "How does Trail Boss express this dislike for jacketed bullets."
I got no reply. Twice.
OK, rant against IMR over.
Since then I understand they have softened their anti-lead position, but see they still provide no plated or jacketed bullet recipes on their web site.
However, this document from Hodgdon has some suggestions
http://www.hodgdon.com/PDF/Trail Boss Reduced Loads R&P.pdf
read paragraph one. It mentions "lead or jacketed" bullets (in reference to rifle cartridges) but does not mention jacketed or plated for handgun cartridges, so recommendations from the maker are still not explicit.
However, my friend and I loaded up some mild loads of TB under his 350 Grain jacketed bullets and they flew out of his 4" S&W 500 Mag at 700 fps. We checked very carefully after each round that the bullet DID exit the barrel. Currently, we stay above 800 fps.
Lost Sheep