Bramble- this might be a very dangerous 'thing' to attempt to copy. Converting a SAA to cap 'n ball is one thing. Trying Trail Boss in a gun originally designed for black powder might be antoehr- and loading it in a rifle might just be disasterous. Trail boss delivers very sedate ballistics, but developes considerable pressure in doing so. It's breech pressures match any other load out there, while delivering su-standard speeds. Just because the velocity is low does not mean the pressure is as well.
: For example, in the .45/70's etc, speeds of over 1,000fps are difficult to achieve, all the while it is developing pressures matching laods that are too heavy for a trapdoor- over 25,000psi. Yes, it's a pussy cat to shoot, BUT - it's pressures are more in line with a tiger's bite.
; Some BP ctg. gun loads latch smokeless for overall breech pressure, BUT black powder developes it's pressure over a very different curve and this pressure curve is why BP guns blow up when using smokeless powders.
; I'd hate to hear of someone who read your initial post and think he can use trail boss in his rifle - or single shot pistol. People do stupid things, not to mention that when polled, 43% of the US baby boomer population indicated they wished to support their retirement from the proceeds of a law suit. That means many are just looking for an excuse to sue someone else.