There are about 20 different propellants in the spectrum between Clays (fastest) to Unique (slowest) pistol/shotgun powders that I would recommend for BP revolver replacement loads. This would include Bullseye, Red Dot, Green Dot, 231,and AA2. 3 to 3.5 grains of any of them will work fine to produce very light loads, but you will have differences in muzzle velocity with identical loads of each. I probably wouldn't go any slower than Unique in this application, as Unique burns more uniformly in heavier loads. On the other hand, at low pressure levels, Unique produces somewhat more smoke than faster propellants, and gives a sort-of Black Powder smokiness, and is therefore popular with the Cowboy Action Shooter clan for use in light .44-40, .44 Special, .44 Magnum, and .45 Colt loads. You will never see fillers recommended for smokeless revolver loads, as the faster propellants ignite and burn fine without it. For example, the most popular and accurate target load for the .38 Special using 148 grain wadcutter bullets is only 2.7 grains of Bullseye, and there is a lot of air left in the powder space behind the bullet. My favorite light load from back in the days I did a lot of CAS was 6 grains of Red Dot, Green Dot, 231, or Bullseye (take your pick) and 240 grain lead SWC bullets in .45 Colt, .44 Special or .44 Magnum cases. They all knocked over the steel plates just fine. Velocities were in the 650-750 fps range. If you are loading shorter cases with less powder space like the .44 Russian, lighter loads would be appropriate to keep the chamber pressures down, and if 3 to 3.5 grains work for you, stop there.
