Further note about T-7 and Pyrodex - they are both made with postassium percolates and their fouling is very hydroscopic - more so than BP fouling. Too, once 'wet' they form corrosives and are very hard on barrels.
Stay with the proven - BP rules.

As to Trail Boss - check the pressures it developes in rifle rounds - it is NOT a low pressure powder - it produces extremely high pressure compared to the low velocities provided.

In a 'little' .45/70 - a mere 13gr.(or so) of it punches pressure up over 23,000PSI. For the 800fps to 900fp produced, that's high indeed. (figures from memory but close)
It certainly does have it's place though - in my .45/60 Sharps, it puts 385gr. cast into the same group at 100yards as a 60gr. load of BP with 506gr. Schmitzers. So - I can practise with clean shooting (no case cleaning - I'm lazy)) with Trail boss with less recoil too, suing the same sight settings & obtaining almost as good accuracy. It does have a place on some loading benches.