max:

The problem with light loads in 45 Colt is that with such a large case you may not achieve a good powder burn. I'll bet you are experiencing a lot of soot on your cases. If so, that is because the load is not developing enough pressure to expand the case fully and seal the chamber. It's not really a problem, but that's what happens with 45 Colt and light loads. That is exactly what Trailboss was developed for, to take up more space with light loads in large cartridges like 45 Colt.

Just for fun I opened up my Speer manual, 13th edition. For 200 grain lead bullets it lists 8.0 grains of Unique as the recommended starting load and 9.5 grains as the Max. So if you want to stay with Unique, you may want to bump your charge up to 8.0 grains. It is still a relatively light load.

For what it's worth, my own standard Smokeless load for 45 Colt is 7.5 grains of Unique under a 250 grain lead Round Nosed bullet. Not exactly a light load, but not a barn burner either. And even with this load I still get a little bit of soot on the cases.