RoyceP
Yep. Open Tops be a mite fickle. Understand, they will shoot well with almost anything you feed 'em. However, if you're after little itty bitty groups, you'll have to play around with load/bullet combinations to find what the gun likes best.
I have a much more simplistic approach these days. I simply load APP 3f to the bullet base. Any bullet. Although my preference for a .38 runs to the 125Gr Truncated Cone. Very Accurate. For the .44 I like a 160Gr RNFP, also quite accurate. The .45 gets Tricky. I really like Cowboy 45 Special cases with 130Gr Barnstormer bullets in .45 Colt chambers. In my conversions, I am running 45 ACP cylinders, with 45 ACP cases (natch) and Barnstormer bullets. Both of which are very accurate. They shoot better than I do.