Regarding the Trailboss - I purchased 2 bottles last week specifically for cowboy action.
5.5 grains of the stuff filled my case almost 60%, and loaded it under a 200 grain LRNFP bullet. Gave me just a little over 700 FPS. I would guess that my .45 cases would only hold about 6.5 grains of Trailboss, and still have enough room for the bullet.
Most likely not enough to get it to the 900 FPS for a 250 grain bullet.
That being said, the loads I used were very mild in recoil,and burned very clean. If you want something to shoot all day to "plink" and practice with, Trailboss will fit the bill.
Otherwise, I have had a lot of luck with Unique, Clays and TiteGroup.