I've done the COW route. I found coffee worked better. COW tends to burn and cake up in the shoulder and had to be cleaned out with a right angle pick. Coffee is already burnt and somewhat better and easier to clean. Smells better too
I would also recommend cleaning every 10 rounds to keep crud out of the neck area. IME
Another alternative to COW is cornmeal. It doesn't seemto cake up or burn in barrel (I have used cornmeal on 500+ fire-formed cases thus far). Any fast-burning pistol or shotgun powder will do the trick.
I like these ideas but wonder about the abrasiveness of them compared to cow. Surely it's still less abrasive than a copper bullet.
I would think trail boss would work since you can just fill a case and stick a lightweight bullet in for reduced loads with no worries. But, cleaning that powder out of a bore is a real bear in my experience. I used it for 10 rounds with Tubbs bullets once and it was a chore just cleaning up from those 10