Pyrodex RS [RS stands for rifle and shotgun] is not a good choice for a handgun. That is why there is Pyrodex P - P for pistol/revolver.
Hodgdons data book states that 21gr BY WEIGHT of Pyrodex P is a good load. If you have a BP measure that operates by weight, then set it to weigh 28gr.
There is no documented data for shooting RS in a handgun.
Others might able to help you out here, but I can't. Sorry.
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