I believe if you increase the MV of your 255 gr loads the POI will move downward toward the POA.I have a few Colt SAA's as well as a few different molds including the Keith molds. One thing I have found is they all shoot 3-4" high with a 255gr and it's hard to file your front sight taller. What I have found to work good and shoot POA/POI is just plain old 200gr SWC that I cast for my 45 ACP's.
I load them light with Titegroup and the are very accurate.
I've heard tell that the original Colt's were tested with 255gr at 50yds but I don't know if that is true.
My advice too. 255 gr lead in front of 8.0 Unique is the "standard load" and will probably take care of most of your needs. I cross check every load I use in SEVERAL reloading manuals before loading and the Lyman #50 is the best reference in my opinion. The Speer manual would be my 2nd choice.255gr lead in front of 8.0gr Unique.
Buy Lyman #50 and read it.
That was my experiences as well; Using a pair of Ruger Vaqueros in cowboy shooting and reducing the loads resulted in the 200 gr bullets shooting low.I have used Unique, W231/HP38 and Titegroup, usually under a 250 or 255 gr RNFP or SWC. I have started to prefer the RNFP since it feeds better in my Rossi 92. I have also gone to the coated bullets.
If you have fixed sights, I have found that the 200 gr bullets do not correspond well to the sights, at least for me.
I don't disagree about the reloading manuals, though nowadays you can pretty much find all the data you need online from the various powder and bullet companies. I read all my reloading manuals (Hornady, Hodgdon, Speer, etc.) from cover to cover in my earlier reloading years, and I found it invaluable to read all the comments, caveats, etc. that were to be found there. It really sets the context in one's mind. As far as just simple load data, however, it's all there online now, at least all one really needs. Since I'm nearly always casting my own bullets, and the particular shapes and weights aren't an exact match to the major manufacturer's bullets used in the load data, I end up interpolating most of my load data anyway.Hodgdons reloading web sight has min-max loads for Hodgdons powders, Usually a couple of preferred Bullitt weight & design,COL, etc. the joy of reloading is finding the pet load for your specific gun. Start at the minimum powder charge, and work your way up very gradually. Make up approximately 5 rounds of each load, and find what works best for you in the specific gun you’re shooting. A quality (current) reloading manual is well well worth the investment, as a lot of new powders may not be listed in the older reloading manuals. Best of luck, and stay safe.