My experience with loading light pistol loads has primarily been with Bullseye in .38 and .45 cast bullet loads. It's a fast powder and does well with target/plinker loads. Between TrailBoss and WSF, TrailBoss has a burning rate closer to that of Bullseye. That's the powder I'd try first. Stick_man may be correct about its bulk/energy, but you indicated that you looking for light loads with the powder you have. I typically use powders around WSP's burning rate in larger revolver cases. YMMV
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