I am loading a Cactus Plains bullet in my 38-55. It is the 265 grain FP Plain Base bullet, sized to .379" [My groove diameter is .377", so about perfect]
These shoot best in my M94 Winchester at about 1400 fps [I use RL 7, but Norma 200 works well also] IMR 4198 works, but not as accurate.
I have had NO leading issues at all, and have driven them right up to 1700 FPS or so.
For low-velocity "plinking" the Trail Boss suggestion is great!
Regards, Eagleye