Sounds to me like your conversions are correct. Many years ago I talked to Hodgdon about this very subject. I was told to use 75% Pyrodex for the equivalent to 100 grains of BP by weight. Volume measurements come into play at the botton of the powder can where the powder is very fine. I always mix my Pyrodex before I load cartridges. Also they told me that the only difference in RS and Select is that the Select is taken from a more consistent batch of powder. Guess that is like Single barrel whiskey from the Jack Daniels distillery.
