I have one, virtually brand new, that wouldn't give me good accuracy, even after throating the chambers. I finally figured out that original Colt .45 loads used a hollowbase bullet. I looked around for one, and found the Lee Modern Minnie mould -- this comes in .450 and .454. I bought the .454 (around $18.00), which throws a nominally 298 grain ball, and did some cogitating.
Using the Hodgdon manual, which lists two sets of data for the .45 ("Regular" and "Ruger only"), I picked powders listed in both sections. The starting and max loads gave me 4 data points, with charge, pressure and velocity for each.
Dumping the data into a graphing function, I found it was all linear. That gave me confidence that I could interpolate, or extrapolate backwards if needed. I arrived at 14 grains of Li'l Gun (chosen because of it's low peak pressures and prolonged peak.) That should give just about 15,000 CUP (close to SAAMI spec for .45 Colt -- and a "regular" load) at just about 1,000 fps.
I discussed this with Ed Harris, and we decided to go a bit lower -- 12 grains. That should produce a few thousand less CUP and something around 900 fps.
The first loads went into 2" at 25 yards, and averaged 875 fps over my Crony chronograph. It's a comfortable load to shoot, as well. I may take a deer with it this season.